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ADDRESS 



CITY 



Southwest Technical Products Corp. 
Box 32040, San Antonio, Texas 78284 




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In This CITE 



ARD PALATE 



NASAL TRACT 
SOFT PALATE 




TONGUE TIP 



page 16 



What's good for about four billion 
bytes on line capacity, 10 to 50 ms 
access time, and a system cost in the 
personal computing category? Find 
out by reading Martin Buchanan's 
article on What Do You Do With a 
Video Disk? 

"Friends, Humans, and Country- 
robots. Lend Me Your Ears." When 
you've reached a point in your audio 
output micro-experimentation where 
the computer can talk, you'll have 
quite an accomplishment. D Lloyd 
Rice describes some of the background 
information needed to create a human 
vocal tract model with computer con- 
trol in his excellent tutorial on the 
subject. Imagine, Star Trek imple- 
mented with a real ship's computer 
output! 

What plugs into one Altair or 
IMSAI compatible bus slot, eats serial 
phoneme snacks, talks back and won't 
shut up till you pull the plug? Find 
out by reading Wirt Atmar's historical 
background and description of a new 
Altair compatible plug-in voice synthe- 
sizer, a commercial version of the 
prototype which was demonstrated as 
a prize winning entry in the recent 
MITS World Altair Computer Conven- 
tion. Once you get the hang of its 
accent, your talking computer will add 
a new dimension to conversational 
software. 



What's wrong with the 8080 pro- 
cessor architecture? Ask a programmer 
for "features" and you'll get some 
answers. An analysis followed by 
definition of improvements resulted in 
the new Zilog Z80 microprocessor 
which is the ultimate in 8 bit micro- 
processors at this point in time. Find 
out what the Z80 is all about by 
reading Burt Hashizume's Micro- 
processor Update: Zilog Z80. 

The act of programming, like any 
act of creation, requires a bit of 
organization and discipline on the part 
of the thinker. In the second reprint 
from Nat Wadsworth's Machine Lan- 
guage Programming for the "8008" 
(and similar microcomputers) you'll 
find some thoughts on the design and 
planning of programs. 

In May BYTE, we had A Date With 
KIM. Here is the next chapter in the 
continuing story of True Confessions: 
How I Relate to KIM. Turn to Yogesh 
M Gupta's account of modifications to 
the KIM-1 system which achieve com- 
patibility with slower memories, bus 
expansion, and a priority interrupt 
capability. 

A sub theme of this BYTE is the 
idea of the talking personal computer 
system. Well, Jack Hemenway and 
Robert Grappel got together recently 
to concoct an allegorical tale of Jack's 
assembler. In Jack and the Machine 
Talk you'll see a dialogue with a 
computer personified. Which leads to 
the next step: Who'll be the first 
reader to create a program to imple- 
ment the computer side of the dia- 
logue, using one of the new voice 
output devices which are coming to 
market? 




Want to experiment with high level 
languages (like APL) that require an 
extended character set? Want to 
simply build and utilize a convenient 
text display output device? Need up- 
per and lower case displays for a text 
editor? If so, and if you can get by 
with a 32 character line on a standard 
TV set or monitor, then Dr Robert 
Suding's latest article will be of in- 
terest. Build a TV Readout Device for 
Your Microprocessor using his detailed 
design. 

What's an |2L? Terry Steeden has 
written a short background summary 
of this relatively new logic family, one 
which has important manufacturing 
and power consumption advantages 
which assure its place in the stable of 
semiconductor fabrication methods. 

Many readers have found real bar- 
gains in older Baudot Teletype 
machines such as the Model 1 5 and the 
Model 19. The main problem, though, 
is Interfacing the 60 mA Current Loop 
to the normal TTL level signals of a 
typical microcomputer. One solution 
to this problem is provided by Walter 
S King's short article in this issue. 

And for the cover, Robert Tinney 
portrays a scene from the near future. 



In the Queue 



BITI #12 

AUGUST 1976 

staff 



Foreground 



44 
66 
96 



TRUE CONFESSIONS: HOW I RELATE TO KIM 

Hardware — Gupta 
BUILD A TV READOUT DEVICE FOR YOUR MICROPROCESSOR 

Hardware — Sliding 
INTERFACING THE 60 mA CURRENT LOOP 

Hardware — King 



Background 



6 
16 
26 
34 
40 
52 
84 



WHAT DO YOU DO WITH A VIDEO DISK? 

Speculation — Buchanan 
FRIENDS, HUMANS, COUNTRYROBOTS: LEND ME YOUR EARS 

Hardware — Rice 
THE TIME HAS COME TO TALK 

Voice Systems — Atmar 
MICROPROCESSOR UPDATE: ZILOG Z80 

Hardware — Hashizume 
MACHINE LANGUAGE PROGRAMMING FOR THE "8008"-Chapter 2 

Software — Wadsworth 
JACK AND THE MACHINE TALK (or, The Making of an Assembler) 

Software — Grappel-Hemenway 
WHAT'S AN |2l (I squared L)? 

Hardware — Steeden 



Nucleus 



2 






In This BYTE 


4 






Some Notes on Clubs 


12 






Letters 


50, 


78, 


83, 




86, 


90, 


98, 




105, 


122 


i 


What's New? 


74 






Book Review 


76 






BYTE's Bugs 


77 






Classified Ads 


81 






Software Bug of the Month 3 


88 






Systems of Note 


95 






Functional Specifications 


100 






Clubs, Newsletters 


126 






Tool Box Answers 


128 






BOMB 


128 






Reader's Service 



PUBLISHERS 

Virginia Peschke 

Manfred Peschke 

EDITOR 

Carl T Helmers, Jr 

GENERAL MANAGER 

Manfred Peschke 

PRODUCTION MANAGER 

Judith Havey 

CIRCULATION 

Deborah R Luhrs 

DEALER CIRCULATION 

Deena Zealy 

PUBLISHERS ASSISTANTS 

Cheryl Hurd 

Caro Kandel 

Carol Nyland 

ADVERTISING 

Elizabeth Alpaugh 

Virginia Peschke 

TYPOGRAPHY 

Custom Marketing Resources, Inc 

Goodway Graphics 

Mary Lavoie 

Taimi Woodward 

PHOTOGRAPHY 

Ed Crabtree 

Custom Marketing Resources, Inc 

ART 

Mary Jane Frohlich 

Bill Morello 

PRINTING 

The George Banta Company 

Custom Marketing Resources, Inc 

ASSOCIATES 

Bob Baker 

Dan Fylstra 

Harold A Mauch 

Chris Ryland 

CONTEST EDITOR 

Janice D Black 



BYTE magazine is published 
monthly by BYTE Publica- 
tions, Inc, 70 Main St, Peter- 
borough, New Hampshire 
03458. Subscription rates are 
$12 for one year worldwide. 
Two years, $22. Three years, 
$30. Second class postage paid 
at Peterborough New Hamp- 
shire 03458 and at additional 
mailing offices. Phone 
603-924-7217. Entire contents 
copyright 1976 BYTE Publica- 
tions, Inc, Peterborough NH 
03458. Address editorial cor- 
respondence to Editor, BYTE, 
70 Main St, Peterborough NH 
03458. 



Some Notes on Clubs 



Editorial by Carl Helmers 



Mapping Sessions 

On April 28 1976 I attended one of the 
biweekly meetings of the Homebrew Com- 
puter Club in Palo Alto CA with Dave 
Fylstra and Mike Wilbur of Stanford Re- 
search Institute as my guides. The meeting 
was most interesting from several points of 
view. One of the best features was the 
session of "mappings" which occupied the 
first portion of the evening's activity. This 
activity is one which would be well worth 
instituting by clubs elsewhere, so I'll des- 
cribe my impressions. 

The mapping session provides a mecha- 
nism for various members to advertise what 
they personally have to offer or what they 
are personally looking for. It is a way for the 
persons attending the meeting to find other 
persons with similar (or complementary) 
interests so that they can get together for 
exchanges of software, surplus components, 
expertise in fixing bugs, etc. 

The key to the mapping session is a large 
set of people (in the Homebrew Computer 
Club, n=^400) and an efficient "moderator" 
to coordinate the session (in the Homebrew 
Computer Club meeting of April 28, this was 



TOWARD SPEECH INPUT? 

Speech by computers is now quite possi- 
ble and reduced to the form of output 
peripherals which can be commercially pur- 
chased. The problem of "pattern recogni- 
tion" as applied to human speech inputs is a 
more difficult problem. For an excellent 
background tutorial on the subject of speech 
recognition, see an article by George M 
White of the Xerox Palo Alto Research 
Center, page 40 of the May 1976 IEEE 
Computer magazine. (Any good engineering 
library should have a subscription to this 
publication as well as the other technical 
journals of the IEEE). 



Lee Felsenstein). The moderator selects 
individuals who have raised hands to indicate 
they have an announcement. (The mecha- 
nism would obviously not work if everyone 
yelled at once.) Once recognized, the indi- 
vidual selected stands up, states his or her 
name, gives a short description of interests 
for the evening, then sits down. The purpose 
of standing up is to allow others in the 
audience to get a visual fix on the person so 
that he or she can be located during a 
"random access" session at the end of the 
meeting. After each announcement, the 
moderator selects another person from those 
with pending announcements. 

The moderator also serves to smooth out 
the process in several ways. Since various 
people do not speak clearly enough to be 
heard throughout the assemblage, the 
moderator will often summarize and repeat 
the person's request through the PA system 
if quizzical looks are perceived at various 
places in the gallery. Sometimes, if the topic 
of the person's announcement is exciting or 
generates extreme interest in the audience, 
the moderator can decide to obtain an 
informal poll of interested persons by asking 
for a show of hands. Also, if a long winded 
person gets the floor, the moderator has the 
crucial function of cutting off the speaker if 
necessary, using a polite but firm approach. 
Detail discussions are the province of small 
groups of interested persons getting together 
later in the evening, and are to be avoided 
during the mapping session. 

The announcements people offer include 
fixes of hardware problems, special interest 
applications areas, personal surplus hardware 
or parts, copies of personal software, etc. 
For example, at the April 28 meeting, Tom 
Pittman, author of a Tiny BASIC for the 
6800 processor, stood up and described the 
fact that he had it available with paper tape 
code and documentation in a package cost- 
ing a nominal $5. [See page 76 of July 



Continued on page 126 



SUPER CHPi 

TheZ-80CPUbyZilog 




From The Digital Group, of course. 



If you are considering the purchase of an 8080-based sys- 
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original 8080 — combining all the advantages of the 6800, 
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What's even better . . . the Z-80 is being brought to you by 
The Digital Group — people who understand quality and 
realize you expect the ultimate for your expenditure. With 
the Z-80, combined with the Digital Group System's video- 
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Take a look at some specifications: 

Z-80 FEATURES 

• Complete compatibility with 8080A object code 

• 80 new instructions for a total of 1 58 

• 696 Op codes 

• Extensive 16-bit arithmetic 

• 3 Interrupt modes (incl 8080), mode 2 provides 128 
interrupt vectors 

• Built-in automatic dynamic memory refresh 

• Eleven addressing modes including: 

Immediate 

Immediate extended 

Page Zero 

Relative 

Extended 

Indexed 

Register 

Implied 

Register Indirect 

Bit 

Combination of above 



• New Instructions (highlights): 

Block move up to 64k bytes memory to memory 
Block I/O up to 256 bytes to/from memory directly 
String Search 
Direct bit manipulation 

• 22 Registers — 16 general purpose 

• 1, 4, 8 and 16 bit operations 

DIGITAL GROUP Z-80 CPU CARD 

• 2k bytes 500ns static RAM 

• 256 bytes EPROM bootstrap loader (1702A) 

• 2 Direct Memory Access (DMA) channels 

• Hardware Interrupt controller 

Supports all 3 modes of interrupt 
Mode 2 supports 128 interrupt vectors 

• Data and Address bus lines drive 30 TTL loads 

• Z-80 runs at maximum rated speed 

• Single step or single instruction step 

• EPROM de-selectable for full 64k RAM availability 
(programs may start at location 0) 

• Complete interchangeability with Digital Group 8080A, 
6800 and 6500 CPUs 

The Z-80 is here. And affordable. Prices for complete Digital 
Group systems with the Z-80 CPU start at $475. For more 
information, please call us or write. Now. 



THE DIGITAL GROUP INC. 




PO. BOX 6528 
DENVER.CO 80206 
(303)861-1686 



What Do You Do With a Video Disk? 



Martin Buchanan 
2040 Lord Fairfax Rd 
Vienna VA 22180 



The new video disk 
technology will probably 
be "write only once" 
memory. But that won't 
matter much, for with es- 
sentially infinite storage 
(50^ per billion bytes) you 
can store each new version 
of a program at a new 
physical location until the 
disk is full. Then you start 
a new disk. 



In one to three years, for less than 
$1,000, you should be able to buy a mass 
storage system with the following 
characteristics: 

Directly accessible in 10-50 ms. 

Data transmission rate of 15,000,000 bits 
per second. 

On line capacity of 4,000,000,000 bytes. 

Storage units costing $2 each. 

The only limitation on the first such 
systems may be a "write once" limitation. 
Once something is recorded, it is recorded 
permanently. A California engineering con- 
sultant has told me that this limitation can 
be overcome, but I haven't researched the 
suggested techniques. The limitation isn't 
particularly serious because essentially in- 
finite storage (50^ per billion bytes!) will 
allow you to store each new version of a file 
or program in a new location. Not writing 
over old versions of files and programs will 
certainly aid documentation. 



Table la: Systems. 



The key to this technology is "video- 
disks." Several companies, here and abroad, 
have developed home videoplayers, all using 
disks as their recording medium. Two main 
types are in competition. RCA uses varia- 
tions in capacitance to record information 
with an arm and head which track the 
grooves and pick up the signal. The RCA 
disks can only be accessed serially (sequen- 
tially); like a magnetic tape or audio cas- 
sette, to access a record you must pass over 
all the records between the desired record 
and your present position. Philips and MCA 
Discovision have developed optical players 
which use a laser to scan the disk. Informa- 
tion is stored in "micropits" less than a 
micron in diameter which produce changes 
in the beam detected by photodiodes. These 
optical systems are direct access. The user 
can address any frame and access it quickly, 
regardless of the present position of the 
mechanism. Both systems are scheduled for 



low speed 
audio cassette 
interface 



system access on line data rate access 

cost type capacity (bits/sec) time 
(Kbytes) 

<$100 serial 25-540 110-600 seconds to minutes 



Processor 
Technology 
CDS-VIM last 
cassette system 



serial 128 1200 seconds to minutes 



Altair 88 DCDD 
disk kit (incl. disk 
controller, disk 
drive, one floppy 
disk and software 
controller) 



$1480 direct 300 250,000 400 msec average 



digidisk system 



-$1000 direct 4,000,000 15,000,000 30 msec average 



marketing in late 1976. The RCA system has 
a projected price of $400 and the Discovi- 
sion system, $500. Both systems are players 
only, for use with existing color television 
receivers. 

The Discovision system will store 36,000 
color video frames on a 12 inch floppy 
plastic disk. At roughly a million bits per 
frame, such disks can be expected to hold 
over four billion bytes if adapted for digital 
storage. The disk will rotate at 1500-1800 
rpm. This implies an average latency time of 
less than 20 ms. Assuming an average seek 
time and transfer time of 10 ms yields an 
average access time of 30 ms. 15 mbps is a 
very high data transmission rate and is best 
handled by conversion to 8 bit or 16 bit 
words read in parallel to interface via direct 
memory access to semiconductor main mem- 
ories. A digital system for personal com- 
puting will also require a write capability, a 
laser precise enough and powerful enough to 
burn new information into the disk. Pos- 
sibly, the same laser can be used both to 
read and write, at different power levels. I 
make a projection that the added write 
capability, software for controlling the sys- 
tem and smaller production runs will result 
in a system cost of $1000. Estimates of the 
cost of videodisk production run as low as 
504 per disk. I've projected an end user cost 
of $2 each for blank disks for the digital 
system. A nice amount of information to 
store on the "digidisk" is 2 32 bytes, the 
number addressable by 32 bits, just over 
four billion. 

Table 1 compares this hypothetical sys- 
tem with systems presently available for 
home computers. There are three main 
classes of computer memory. Main memory 
is fast, expensive and directly addressable by 
the CPU. RAM and ROM memories are 
accessible in several hundred nanoseconds 
and cost 2-64 per byte. Secondary storage is 
less expensive and directly accessible in less 



Table lb: Media. 



Table 2: Information Formats in Omnidisk System. 

1. Color video. 

2. Black and white video (can use color format but is wasteful). 

3. Digital storage (2 3 2 bytes). 

4. Music or voice (one or several channels). 

5. High resolution black and white frames to replace microfilm and fiche in libraries 
and homes. 



than a second. Magnetic drums and disks are 
secondary storage devices. Their speed al- 
lows use in virtual memory systems where 
the operating system software moves pro- 
grams and program storage in and out of 
main memory as needed, freeing the user 
from having to program around severe 
memory restrictions. External storage is least 
expensive, but is accessed serially, making it 
unsuitable for use in virtual systems. Magne- 
tic tape, paper tape, punched cards, and 
audio cassette are all serially accessed ex- 
ternal storage media. External storage is used 
for storing programs and data when not in 
use. Optical storage of the type projected 
here will be directly accessible for use in 
virtual systems, will be faster than floppy 
disks, will be 10,000 times cheaper per byte 
of storage, and nearly 1,000 times cheaper 
per byte of on line capacity. 

A more useful but more expensive system 
will be capable of accessing all or several of 
the five types of information in table 2. 
Several types of information can be stored 
on a single disk. For example, a book or 
music library could come with the software 





storage unit 
and cost 


approximate 
cost (4/byte 
of storage) 


approximate 

cost (tf/byte of 

on line capacity) 


low speed interface 


audio cassette 
$1-2 


4-40 x 1 0" 4 


2 x 10" 2 


Processor 
Technology 
fast system 


C30 cassette 
~$1 


5 x 1 0" 4 


more than a low sp 
interface, but fasti 


Altair 88 DCDD 


floppy disk 
$15 


5x 10" 3 


5x 10" 1 


digidisk 
system 


optical disk 
~$2 


~5x 10" 8 


-2.5 x 10" 5 



The most likely video disk 
technology to be ap- 
plicable in mass storage 
areas will be the Dis- 
covision laser system of 
Philips and MCA, since it 
has direct access capability 
and a potential adaptation 
to allow writing of infor- 
mation in a personal 
system. 



One problem of optical 
disks is their sheer 
abundance of data storage 
capacity. 



The overhead per unit of 
information will decline, 
though. It does not take 
10,000 times as much soft- 
ware to access 10,000 
times as much data. 



to access it. Input and output will be 
possible in all formats under microcomputer 
control. Interesting esthetic effects will be 
possible. You will be able to program your 
system so your TV interprets music as a 
color pattern, or displays complex and 
flickering hypnotic bit patterns as your 
computer operates. 

Some Long Range Speculations 

Cheap storage implies that wasteful but 
marginally more useful data structures will 
be used. Hash codes and bit manipulation 
may be unknown to most users of the next 
generation of home computer systems. One 
problem with optical disks is their sheer 
abundance of capacity. It would be clumsy 
to send a 15 minute tape to a friend on a 
disk which can hold hundreds of hours of 
music or voice. What you will do instead is 
tape simultaneously into your corres- 
pondence disk and a cassette, mail the 
cassette to a friend who plays it into his 
correspondence disk as he listens and who 
can then reuse the cassette. 

Larger storage implies more complex data 
structures. A small conventional disk system 
that I use now has the following hierarchy of 
structures: 

(magnetic disk) 
group 
library 
file 

record 
word 

Cataloging, indexing, and writing the soft- 
ware to access the wealth of information in 
existence will be an important profession. 
The overhead per unit of information will 
decline, though. It does not take 10,000 
times as much software to access 10,000 
times as much data. 

Electro Optical Libraries 

I believe this new storage medium will be 
so convenient that it will replace conven- 
tional libraries. The first generation library 
system will be photographic, each page the 
equivalent of one or more video frames 
depending on the desired resolution. Black 
and white images will satisfy most demands 
and higher resolution than TV will be 
desirable. 10 — 40,000 pages will be stored 
on each disk, the equivalent of 50 — 200 
books. This kind of system will resemble 
microfiche in its storage capacity but will be 
directly accessible in milliseconds. The first 
file on the disk will be the software for 
reading the disk and a lookup table which 
tells the computer where each title begins. 
This is an application of the omnidisk 



system. Lawyers, doctors, architects and 
engineers will be among the first users as 
their professional libraries become available 
on optical disk. Converting existing fiche 
and film to the new medium will be done by 
machine. Putting the Library of Congress 
onto optical disk will be tedious and expen- 
sive if photographed by hand. A robot 
camera with demand feed conveyer, waldos 
for turning pages and automatic focussing 
and alignment would be useful for con- 
verting large libraries. Such a library could 
require 10,000 disks, and will require a more 
complex system to make the system fast and 
economical. At least one prototype disk 
system has been develop d with an auto- 
matic feeding mechanism. The principle can 
be applied to constructing a college or 
university system with the following 
elements: 

1. 100 high resolution CRTs for accessing 
material, 

2. A read only multiple player which can 
play up to 100 disks simultaneously, 

3. A disk store accessed by the multiple 
player under computer control. 

If a user requests material on a disk other 
than the one he is currently using, his 
current demand is deleted, a disk that is not 
being used is returned to the store if drive 
space is needed, and the disk with the 
requested material is brought on line. If a 
user requests a disk being used by another 
user, they can both read from it in a 
timesharing arrangement. The system will be 
virtual. The user accesses material in the 
same way whether or not it is on line 
(though it may take several seconds to bring 
new disks on line). Bigger optical storage 
records can make the system faster and 
cheaper. 

The average book can be ASCII coded in 
about 5 million bits. In this form, one 
optical disk could hold 6400 books. Each 
book will cost less than a tenth of a cent to 
produce (compare with present photocopy- 
ing costs of several cents per page, and with 
skyrocketing book prices). It will take less 
than a second for the system to read or write 
an entire book. ASCII text and high resolu- 
tion photos (for illustrations, graphs and 
diagrams) can be interleaved on the same 
disk along with the software for controlling 
access. The Library of Congress will fit in a 
filing cabinet, but to economically convert it 
to ASCII records, you need advances in 
optical character recognition so a robot can 
scan a printed page and read the characters. 



Continued on page 15 



8 



If you thought a rugged, 
professional yet affordable 
computer didn't exist, 



think 
IMSAI 

8080. 



Sure there are other commercial, 
high-quality computers that can 
perform like the 8080. But their 
prices are 5 times as high. There is 
a rugged, reliable, industrial com- 
puter, with high commercial-type 
performance. And prices that are 
competitive with Altair's hobbyist 
kit. The IMSAI 8080. Fully assem- 
bled, it's $931. Unassembled, it's 
$599. And ours is available now. 

In our case, you can tell 
a computer by its cabinet. The 
IMSAI 8080 is made for commer- 
cial users. And it looks it. Inside 
and out! The cabinet is attractive, 
heavy-gauge aluminum. The 
heavy-duty lucite front panel has 
an extra 8 program controlled 
LED's. It plugs directly into the 
Mother Board without a wire 
harness. And rugged commercial 
grade paddle switches that are 
backed up by reliable debouncing 
circuits. But higher aesthetics on 
the outside is only the beginning. 
The guts of the IMSAI 8080 is 
where its true beauty lies. 

The 8080 is optionally 
expandable to a substantial system 
with 22 card slots in a single 
printed circuit board. And the 
durable card cage is made of 
commercial-grade anodized 
aluminum. The Altair kit only 
provides 16 slots maximum in four 
separate sections, each section 




requiring 200 solder connections. 

The IMSAI 8080 power 
supply produces a true 28 amp 
current, enough to power a full 
system. The Altair produces 
only 8 amps. 

You can expand to a 
powerful system with 64K of 
memory, plus a floppy disk con- 
troller, with its own on board 
8080 -and a DOS. An audio tape 
cassette input device, a printer, 
plus a video terminal and a 
teleprinter. These peripherals will 
function with an 8-level priority 
interrupt system. IMSAI BASIC 
software is available in 4K, 




that you can get in 
PROM. And a new $139 4K 
RAM board with software 
memory protect. 

Find out more about the 
computer you thought didn't 
exist. Get a complete illustrated 
brochure describing the IMSAI 
8080, options, peripherals, soft- 
ware, prices and specifications. 
Send one dollar to cover handling. 

Call us for the name of the 
IMSAI dealer nearest you. 

Dealer inquiries invited. 

wba 

IMS Associates, Inc. 

14860 Wicks Boulevard 
San Leandro, CA 94577 
(415) 483-2093 



^B 



Imagine a microcomputer 

Imagine a microcomputer with all the design 
savvy, ruggedness, and sophistication of the best 
minicomputers. 

Imagine a microcomputer supported by dozens 
of interface, memory, and processor option boards. 
One that can be interfaced to an indefinite number 
of peripheral devices including dual floppy discs, 
CRT's, line printers, cassette recorders, video dis- 
plays, paper tape readers, teleprinters, plotters, 
and custom devices. 

Imagine a microcomputer supported by exten- 
sive software including Extended BASIC. Disk 
BASIC, DOS and a complete library of business, 
developmental, and industrial programs. 

Imagine a microcomputer that will do everything 
a mini will do, only at a fraction of the cost. 

You are imagining the Altair 1 " 8800b. The Altair 
8800b is here today, and it may very well be the 
mainframe of the 70's. 

The Altair 8800b is a second generation design 
of the most popular microcomputer in the field, 
the Altair 8800. Built around the 8080A micro- 
processor, the Altair 8800b is an open ended 
machine that is compatible with all Altair 8800 
hardware and software. It can be configured to 
match most any system need. 



NOTE: Altair is a trademark ot MITS. Inc. 





SCQSttP SEDEEItb 




Redesigned front panel. Totally synchro- 
nous logic design. Same switch and LED 
arrangement as original Altair 8800. 
New back-lit Duralith (laminated plastic 
and mylar, bonded to aluminum) dress 
panel with multi-color graphics. New 
longer, flat toggle switches. Five new 
functions stored on front panel PROM 
including: DISPLAY ACCUMULATOR (dis- 
plays contents of accumulator), LOAD 
ACCUMULATOR (loads contents of the 
8 data switches (A7-AO) into accumulator) 
OUTPUT ACCUMULATOR (Outputs con- 
tents of accumulator to I/O device 
addressed by the upper 8 address 
switches), INPUT ACCUMULATOR (in- 
puts to the accumulator from the I/O 
device), and SLOW (causes program 
execution at a rate of about 5 cycles per 
second — for program debugging). 



Full 18 slot motherboard. 

Rugged, commercial grade Optima 
cabinet. 



- New front panel interface board buffers 
all lines to and from 8800b bus. 

-Two, 34 conductor ribbon cable assem- 
blies. Connects front panel board to front 
panel interface board. Eliminates need 
for complicated front panel/bus wiring. 



New, heavy duty power supply +8 volts 
at 18 amps, + 18 volts at 2 amps, 18 volts 
at 2 amps. 110 volt or 220 volt operation 
(50/60 Hz). Primary tapped for either 
high or low line operation. 



■New CPU board with 8080A micro- 
processor and Intel 8224 clock generator 
and 8216 bus drivers. Clock pulse widths 
and phasing as well as frequency are 
crystal controlled. Compatible with all 
current Altair 8800 software and 
hardware. 



altair 8800-b 



MITS, Inc. 1976/2450 Alamo S.E. /Albuquerque, New Mexico 87106 




Letters 



Very soon the interest is 
going to shift from "what 
to buy" and "how to get it 
going" over to "what to 
do with it." 




COMPILER INPUTS NEEDED 

Do you have space at the front of your 
Letters column for this request? [Yes.] 

I'm writing a compiler for 8080 systems, 
and I'd like to know what everybody would 
like to have in it. I'm personally leaning 
towards PL/I, which is my favorite language, 
but the compiler will be able to accept 
FORTRAN as well. = 

Would everybody take a moment to write 
me and tell me what they'd like to see in a 
new compiler? I'll try to put in all the 
routines you can think of. 

And please, don't be afraid to write 
simply because you think somebody else 
might, or you're too "new at the game." 
Although I've been an IBM systems engineer, 
I also spent several years as a disc jockey in 
St Louis and Kansas City. No matter who 
you are, your ideas need to be put into this 
compiler. 

Peter Skye 

Chief Engineer 

Watermark Inc 

10700 Ventura Blvd 

No Hollywood CA 91604 

(213)980-9490 

Let us know when it's ready. 

EMULATION, ANYONE? 

I just finished reading the literature on 
the new PCM-12 microcomputer which uses 
the Intersil IM6100 MPU that recognizes the 
Digital Equipment Corporation PDP-8 
instruction set. It occurs to me that a very 
worthwhile software development project 
for the home microcomputer system would 
be an interpretive translator/emulator pro- 
gram that would allow the microcomputer 
to run DEC's PDP-8 software (ie: program 
would input a single 12 bit PDP-8 instruc- 



tion and then output one or more micro- 
computer 8 bit instructions which would be 
immediately executed and accomplish the 
same task). This would allow the hobbyist to 
take advantage of the huge mountain of 
software developed for this very popular 
minicomputer, which includes such high 
level languages as BASIC, FORTRAN, 
ALGOL, FOCAL, etc. Most of the software 
is available over the counter from DEC for a 
very nominal charge. 

Because the architecture of the PDP-8 is 
based on a 12 bit word, the 8 bit micro- 
computer would have to operate on each 
word as two 6 bit half words stored in 
consecutive locations. The main disadvan- 
tage with this emulator method would lie in 
the increased memory length and execution 
time required. 

I would like to see some dialogue started 
in the pages of BYTE on the desirability and 
feasibility of a program such as this. Some 
prime candidates for translators would be 
microcomputer systems based on the 8080, 
M6800, and MCS6500 (especially the latter 
since no high level languages exist for this 
unit, but a number of very low cost systems 
are available). 

Don B Keek J r 

Senior Engineer, Loudspeakers 

ElectroVoice Inc 

600 Cecil St 

Buchanan Ml 49107 

Is anyone doing such an emulation? 
Rumor has it that at least one or two 
PDP-11 emulators are around running on 
8080s and the like, and the technical chal- 
lenges of a PDP-8 version cannot be any 
worse. 

CRITIQUE AND SUGGESTIONS 

Your article in the March BYTE "Assem- 
bling Programs by Hand" [page 52] was 
very pertinent and timely. It's probably the 
method most of your readers will be using. 

The actual "how to do it" part was well 
done and allowed rather complete compre- 
hension by most of your readers. But the 
first part of the article setting up the 
example to work on was probably beyond 
most of your readers, at least those who did 
not come up through programming. Either a 
simpler example or more explanation of the 
example used would have made the article 
even more valuable. 

We see much written on interfacing to 
peripherals such as TTY, TV keyboards, tape 
cassettes, etc, which, of course, is needed. 
But isn't it time to start going into some of 
the other functions a growing number of 



12 




The intecolor 8001 Kit 

A Complete 8 COLOR intelligent CRT Terminal Kit 



$1,395 



"Complete" Means: 

• 8080 CPU • 25 Line x 80 Characters/Line • 4Kx8 RAM • PROM 
Software • Space for UV Erasable PROM • 19" Shadow Mask 
Color CR Tube • RS232 I/O • Selectable Baud Rates to 9600 
Baud • Single Package • 8 Color Monitor • ASCII Set* Keyboard 

• Bell • Manual 

And you also get the Intecolor" 8001 9 Sector Convergence 
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Additional Options Available: 

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• Light Pen • Limited Graphics Mode • Background Color 

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Delivery 30-60 days ARO. 
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ISC WILL MAKE A BELIEVER OUT OF YOU. 



Send me. 



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plus $15.00 shipping charges each. 
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Shipment for $ 

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on personal checks. 



intelligent Systems Corp. 

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Telephone (404) 449-5961 



® 



Should I do it in hardware 
or software? 



Nothing compares with 
the satisfaction of exercis- 
ing complete control over 
a small universe which can 
be tailored and operated 
to suit one's needs. 



your readers will become interested in? For 
example, I would think a number of readers 
will be wanting to control some interrelated 
physical quantities which are measured with 
digital and analog sensors/transducers (digi- 
tal tachometers, digital flowmeters, tempera- 
ture sensing, etc). Hence a detailed article on 
processing input pulse trains might be well 
received. The reverse, an in depth article on 
outputting pulse trains to move something 
via a stepping motor (now relatively inex- 
pensive) should be equally popular. Many 
readers might be interested in inexpensive 
AD inputs. Although Motorola covered this 
subject well in their AN-757 note for the 
6800, it could still be "interpreted" to your 
readers. 

All of this could pave the way for some 
articles on dedicated digital control systems 
which should be intriguing to your readers as 
they grow in sophistication. I say all this 
because it would seem that very soon the 
interest is going to shift from "what to buy" 
and "how to get it going" over to "WHAT 
TO DO WITH IT." 

Gordon March 
Cedar Rapids IA 

Potential authors take note. Gordon 
March has some good suggestions to make, 
concerning both implementation and choice 
of subject matter of articles. 



ANOTHER ARTICLE IDEA 

I think BYTE is fantastic. I have been 
thinking about writing a little algebraic 
expression processor for several years now 
but could never figure out how to exactly. 

When I got February and March issues of 
BYTE and read the articles on Processing 
Algebraic Expressions [page 26, February; 
page 62, March], things started clicking 
into place. Now all I have to do is test it on 
the college's Univac 1 1 06 and see if it works. 

I don't have a micro yet and probably 
won't get one for a few years. When I do, it 
will probably be based on Intel's 3000 series 
because I want to be able to define my own 
instruction set. It would be very helpful if 
you had an article on this family of chips. 

R Tim Coslet 
Phoenix AZ 

YE OLDE HARDWARE - SOFTWARE 
TRADEOFF 

I was very impressed with Mr Frank's 
novel approach to the design of analog to 
digital convenors. For those who missed the 
May 1976 issue, he suggested [page 70] 



using a microprocessor for the feedback 
element of an ADC. This technique has the 
advantages of being inexpensive, and very 
simple to put together. However my applica- 
tions for ADC require higher speeds (20 
kHz) and complex data reduction. In light of 
these requirements, CPU control of the ADC 
loop is too slow, and wasteful of processor 
time. Essentially all the processor is doing is 
acting as an Up/Down Counter, at least in 
the "Tracking" configuration. Therefore, at 
a slight increase in cost, I would replace the 
processor as control element, with the 
appropriate MSI TTL packages (ie: 74193). 
This has the effect of greatly speeding up the 
conversion time, and unburdening the proc- 
essor so it can do its thing in between sample 
times. The question boils down to the old 
one: "Should I do it in hardware or soft- 
ware?" The answer is not usually an obvious 
or easy one; but my experience tells me to 
try hardware first, if the costs are almost the 
same. Microcomputers can have a hard time 
keeping up with real time, and my impulse is 
to try to ease their minds by doing some of 
the work outside in supporting circuitry. 
The difficult part is making sure the total 
system gets the maximum effectiveness from 
each component part. 

Ira Rampil 

University of Wisconsin 

Dept. of EE and CE 

Madison Wl 53706 

PS: The Motorola Linear IC Data Book, 3rd 
edition, has a nice section on applications of 
their data conversion chips. 

YOUOLDTSOANDTSO! 

I don't think that anyone has thus far 
mentioned in BYTE the single greatest 
impetus for DP professionals like myself to 
take up personal computing. That impetus is 
frustration. The amateur cannot appreciate 
how frustrating it can be, even irr a multi- 
CPU shop. There is slow batch turn-around 
time, slow TSO response time, missing print- 
outs, lost decks, and of course the inevitable 
system down time .... not to mention the 
restraints of system standards, rules, and 
regulations. 

It is so satisfying to turn on one's own 
system, input through its console, and enjoy 
instantaneous response. There is nothing to 
compare with the satisfaction of exercising 
complete control over a small universe which 
can be tailored and operated to suit one's 
needs. And there is the sense of freedom in 



Continued on page 108 



14 



Continued from page 8 

When your children get good grades, you 
won't get them a Brittanica, but a Universal 
Data Base, a compendium of human know- 
ledge made up of several thousand selected 
books. 

What about music? One optical disk will 
be able to record hundreds of albums. 
Around 1980 you may see and hear this ad 
on your TV: 

"Discomania! The complete works 
of the Beatles, Cat Stevens, Beethoven, 
Johnny Cash, the Mormon Tabernacle 
Choir, and many many more! Just 
send your name and address, check or 
money order for $9.95 to ... or 
call ... toll free to order your copy 
now. Hurry, hurry. Our supply is 
limited." 

Problems of Copyright 

Works in the public domain like classical, 
religious, and ethnic music will be quickly 
offered once the technology is widely avail- 
able. Pirates could have a field day with 
easily copied disks. Duplicating a rock and 
roll collection costing hundreds of dollars, 
putting it on one disk and making a killing 
could become quite enticing to unethical 
individuals. Copyright conventions will have 
to evolve and adapt to this medium as it 
becomes available. 

Education via Disk 

With versatile inexpensive mass storage 
media, correspondence schools might evolve 
into a new form. You might receive one or 
more disks containing: 

text, 

pictures and film clips where needed, 
voice for language lessons, 
all the software necessary for im- 
mediate interactive examinations and 
correction of mistakes, including a 
diagnostic exam at the start of the 
course, and a final at the end. 

For language courses you may be able to 
buy a voice analyzer that digitizes your voice 
response so the software can check your 
pronunciation. 

Present schools will be obsolete as the 
free market provides the tools for a superior 
form of education. The home computer will 
teach better and faster, providing individual 
attention. 



The average book text can 
be ASCII coded in about 
five million bits. In this 
form, one optical disk 
could hold 6400 books. 



The compulsory education laws will prob- 
ably be reduced to the requirement of a 
yearly examination covering basic subjects. 
For poorer families, there will be neighbor- 
hood computer centers (lots of space and 
low rents in those deserted former schools) 
with perhaps ten children using each 
terminal during the week, each with his or 
her own software library and keyword. 

Long Distance Communications 

With millions of computers in homes and 
small businesses, the market for cheap long 
distance communications will open up. My 
computer in DC will talk to your computer 
in California via phone hookups to DC and 
Los Angeles data transmission centers which 
send information across the country. There 
is one present bottleneck: Phone lines can't 
handle high data rates. They are for audio 
signals, and signals at 1 kHz or so are 
extremely slow compared to a potential 15 
MHz video disk. With 10^ gigahertz of 
bandwidth via laser networks you could 
reserve 20 MHz for every computer in the 
country. That requires optical circuitry now 
being developed. Eventually the present hard 
wired phone technology will be supple- 
mented and then superseded by a fiber optic 
network. 

With large cheap optical storage, new 
levels of reliability will be cheap and desir- 
able. Parity bits and error checking codes 
will be in vogue. 

The postal service may go the way of the 
pony express. The network made economic- 
al by computer traffic will also carry the 
daily paper, BYTE, and first class mail. Why 
physically transport data if an energy saving 
electronic communication does the same 
thing? Data privacy will be easy to secure. 
With cheap storage you can generate your 
own "one time pad," a cipher which cannot 
be broken because it uses an infinite cipher 
alphabet. Ciphering and deciphering will be 
computerized. 

With cheap processors and unlimited 
cheap fast memory, what can't we do? The 
effects on individuals and society will be 
major and sometimes unexpected. Today's 
personal computer is but a first step in this 
trend toward sophisticated applications. 



Why physically transport 
data such as letters and 
books if an energy saving 
electronic communications 
medium can accomplish 
the same thing? 



15 



HARD PALATE 



NASAL TR 
SOFT PALATE 



VELUM 
ORAL TRACT 
TONGUE BODY 



NOSTRILS 




TONGUE TIP 



Figure I: The Human Vocal Tract. The 
human vocal tract is roughly described as a 
tube approximately 17.4 cm long with 
varying resonance characteristics as muscles 
control the shape. The tract splits into two 
parts, nasal and oral, at the top, with a valve 
called the velum providing flexible control 
of the nasal resonances in given utterance. 
An electronic model of this natural organ 
roughly parallels the function of the tract. 



















































DESIRED 








y 








CURVE 






~"">d 


w "B!^ 














A 




















,-*i 













































ACTUAL 
DAC OUTPUT 



Figure 2: DA C Quantization Errors. The actual output of a computer to the 
analog world is a step function (in the absence of any filtering). This leads to 
the problem of quantization errors, depicted conceptually here by the shaded 
areas in between the smooth analog function and its closest step function 
approximation. Low precision digital to analog conversions accentuate this 
problem. 



Friends, Humans, 



D Lloyd Rice 
Computalker Consultants 
821 Pacific St #4 
Santa Monica CA 90405 



You've got your microcomputer running 
and you invite your friends in to show off 
the new toy. You ask Charlie to sit down 
and type in his name. When he does, a 
loudspeaker on the shelf booms out a hearty 
"Hello, Charlie!" Charlie then starts a game 
of Star Trek and as he warps around thru the 
galaxy searching for invaders, each alarming 
new development is announced by the ship's 
computer in a warning voice, "Shield power 
low!", "Torpedo damage on lower decks!" 

The device that makes this possible is a 
peripheral with truly unlimited applications, 
the speech synthesizer. This article describes 
what a speech synthesizer is like, how it 
works and a general outline of how to 
control it with a microcomputer. We will 
look at the structure of human speech and 
see how that structure can be generated by a 
computer controlled device. 

How can you generate speech sounds 
artificially, under computer control? Let's 
look at some of the alternatives. Simplest of 
all, with a fast enough digital to analog 
converter (DAC) you can generate any 
sound you like. A 7 or 8 bit DAC can 
produce good quality sound, while some- 
where around 4 or 5 bits the quantization 
noise starts to be bothersome. This noise is 
produced because with a 5 bit data value it is 
possible to represent only 32 discrete steps 
or voltage levels at the converted analog 
output. Instead of a smoothly rising voltage 
slope, you would get a series of steps as in 
figure 2. As for the speed of the DAC, a 
conversion rate of 8,000 to 10,000 conver- 
sions per second [The sample rate in con- 
versions per second or samples per second is 
often quoted in units of Hertz. We will use 
that terminology here, although conversions 



16 



and Countryrobots: Lend me your Ears 



per second is a generalization of the concept 
of cycles per second] is sufficient for fairly 
good quality speech. With sample rates 
below about 6 kHz the speech quality begins 
to deteriorate badly because of inadequate 
frequency response. 

Almost any microprocessor can easily 
handle the data rates described above to 
keep the DAC going. The next question is, 
where do the samples come from? One way 
to get them would be by sampling a real 
speech signal with a matching analog to 
digital converter (ADC) running at the same 
sample rate. You then have a complicated 
and expensive, but very flexible, recording 
system. Each second of speech requires 8 K 
to 10 K bytes of storage. If you want only a 
few words or short phrases, you could store 
the samples on a ROM or two and dump 
then sequentially to the DAC. Such a system 
appears in figure 3. 

If you want more than a second or two of 
speech output, however, the amount of 
ROM storage required quickly becomes im- 
practical. What can be done to minimize 
storage? Many words appear to have parts 
that could be recombined in different ways 
to make other words. Could a lot of memory 
be saved this way? A given vowel sound 
normally consists of several repetitions of 
nearly identical waveform segments with the 
period of repetition corresponding to the 
speech fundamental frequency or pitch. 
Figure 4 shows such a waveform. Within 
limits, an acceptable sound is produced if we 
store only one such cycle and construct the 
vowel sound by repeating this waveform 
cycle for the duration of the desired vowel. 
Of course, the pitch will be precisely con- 
stant over that entire interval. This will 
sound rather unnatural, especially for longer 
vowel durations, because the period of 
repetition in a naturally spoken vowel is 
never precisely constant, but fluctuates 
slightly. In natural speech the pitch is nearly 
always changing, whether drifting slowly or 




MICROPHONE 




ADC 










AN 


LOW-PASS 
FILTER 




PROGRAMMABLE 
MEMORY 




ROM 


y * 

























+ 




SPE 




DAC 








ROM 




LOW-PASS 
FILTER 


k r 






*L 











*\z 



Figure 3: Waveform Playback from ROM Storage. One way to achieve a 
digitally controlled vocal output is to first digitize a passage of human speech, 
then store the digital pattern in memory. For a commercial product, such as a 
talking calculator, the limited vocabulary required makes this a feasible 
avenue of design, especially when a single mass produced ROM can be used in 
the final product. In an experimenter's system, the ROM is not needed, and 
programmable memory can be substituted during experiments. This is 
probably the least expensive way to augment an existing computer's 
capability with vocal output, but the memory requirements limit its use to 
small vocabularies. The quality of the result varies with the ADC (and DAC) 
sampling rate and precision. 




Figure 4: Typical Vowel Waveform. In prin- 
ciple, a vowel is a fairly long sustained 
passage of sound with repetitive characteris- 
tics. The vo wel sounds are produced physiol- 
ogically by the resonances of the vocal tract, 
and are controlled electronically by the 
formant filters which produce the equivalent 
of vocal tract resonances. 



17 



ACOUSTIC RESONATOR 
(ONE END CLOSED) 
(ONE END OPEN) 



■ i- 17.4cm- 



VELOCITY OF SOUND, c ■ 34800cm/sec 
Xn. WAVELENGTH OF nTH MODE 
FREQUENCY OF nTH MODE , F n ■ c/ Xn 



FORMANT I 
AIR PRESSURE 
DISTRIBUTION 



Fl ■ '/4J -500Hz 



FORMANT 2 
AIR PRESSURE 
DISTRIBUTION 



I- 3X 2 /4 F2 ■ 3c/4J( . 1500Hz 



FORMANT 3 
AIR PRESSURE 
DISTRIBUTION 



•t-5X 3 /4 F3- 5C/41- 2500 Hz 



Figure 5: Tube Resonances. Temporarily ignore the complicated shape of the vocal tract and 
simplify it to a tube 17.4 cm long. Applying the equations of physics to acoustic waves in air 
gives resonances at several modes or natural frequencies. The standing waves along the tube at 
each frequency are shown, and identified as formant 1, formant 2 and formant 3. In the actual 
vocal tract, a more complicated and time varying geometry changes the resonances as a sound is 
created. 




sweeping rapidly to a new level. It is of 
interest that this jitter and movement of the 
pitch rate has a direct effect on the percep- 
tion of speech because of the harmonic 
structure of the speech signal. In fact, 
accurate and realistic modelling of the 
natural pitch structure is probably the one 
most important ingredient of good quality 
synthetic speech. In order to have smooth 
pitch changes across whole sentences, the 
number of separate stored waveform cycles 
still gets unreasonable very quickly. From 
these observations of the cyclic nature of 
vowels, let us move in for a closer look at 
the structure of the speech signal and ex- 
plore more sophisticated possibilities for 
generating synthetic speech. 

How Do We Talk? 

The human vocal tract consists of an air 
filled tube about 16 to 18 cm long, together 
with several connected structures which 
make the air in the tube respond in different 
ways (see figure 1). The tube begins at the 
vocal cords, or glottis, where the flow of air 
up from the lungs is broken up into a series 
of sharp pulses of air by the vibration of the 



Figure 6: "ah" as in "father." In figure 1, 
the vocal tract was shown in schematic form. 
Here is a similar figure showing how the 
tract has been modified to produce the 
vowel sound "ah. " The human typically 
closes off the nasal cavity and widens out 
the oral cavity by opening the mouth during 
this sound. 



vocal cords. Each time the glottis snaps shut, 
ending the driving pulse with a rapidly 
falling edge, the air in the tube above 
vibrates or rings for a few thousandths of a 
second. The glottis then opens and the 
airflow starts again, setting up conditions for 
the next cycle. 

The length of this vibrating air column is 
the distance from the closed glottis up along 
the length of the tongue and ending at the 
lips, where the air vibrations are coupled to 
the surrounding air. If we now consider the 
frequency response of such a column of air, 
we see that it vibrates in several modes or 
resonant frequencies corresponding to dif- 
ferent multiples of the acoustic quarter 
wavelength. There is a strong resonance or 
energy peak at a frequency such that the 
length of the tube is one quarter wavelength, 
another energy peak where the tube is three 
quarter wavelengths, and so on at every odd 
multiple of the quarter wavelength. If a tube 
17.4 cm long had a constant diameter from 
bottom to top, these resonant energy peaks 
would have frequencies of 500 Hz, 1 500 Hz, 
2500 Hz and so on. These resonant energy 
peaks are known as the formant frequencies. 
Figure 5 illustrates the simple acoustic 
resonator and related physical equations. 

The vocal tract tube, however, does not 
have a constant diameter from one end to 
the other. Since the tube does not have 
constant shape, the resonances are not fixed 
at 1000 Hz intervals as described above, but 
can be swept higher or lower according to 
the shape. When you move your tongue 
down to say "ah," as in figure 6, the back 
part is pushed back toward the walls of the 



18 



throat and in the front part of the mouth 
the size of the opening is increased. The 
effect of changing the shape of the tube in 
this way is to raise the frequency of the first 
resonance or formant 1 (F1) by several 
hundred Hz, while the frequency of formant 
2 (F2) is lowered slightly. On the other 
hand, if you move your tongue forward and 
upward to say "ee," as in figure 7, the size 
of the tube at the front, just behind the 
teeth, is much smaller, while at the back the 
tongue has been pulled away from the walls 
of the throat, leaving a large resonant cavity 
in that region. This results in a sharp drop in 
Fl down to as low as 200 or 250 Hz, with 
F2 being increased to as much as 2200 or 
2300 Hz. 

We now have enough information to put 
together the circuit for the oral tract branch 
of a basic formant frequency synthesizer. 
After discussing that circuit, we will con- 
tinue on in this way, describing additional 
properties of the speech mechanism and 
building up the remaining branches of the 
synthesizer circuit. 

A Speech Synthesizer Circuit 

To start with, we must have a train of 
driving pulses, known as the voicing source, 
which represents the pulses of air flowing up 
thru the vibrating glottis. This could be 
simply a rectified sine wave as in figure 8. To 
get different voice qualities, the circuit may 
be modified to generate different waveform 
shapes. 

This glottal pulse is then fed to a se- 
quence of resonators which represent the 
formant frequency resonances of the vocal 
tract. These could be simple operational 
amplifier bandpass filters which are tunable 
over the range of each respective formant. 
Figure 9 shows the concept of a typical 
resonator circuit which meets our require- 
ments. IC1, IC2 and IC4 form the actual 
bandpass filter, while IC3 acts as a digitally 
controlled resistance element serving to vary 




Figure 7: "ee" as in "heed." In contrast to 
figure 6, when the "ee" vowel sound is 
created, the mouth opening tends to be nar- 
rowed; and the upper end of the vocal tract 
is restricted. This lowers the frequency of 
the first resonant mode and raises the 
frequencies of the second and third. Refer- 
ring to table 1, the "ee" vowel sound has 
some of the highest resonances for formants 
F2 and F3 and the lowest for FJ. 





DATA BUS 



Figure 8: Voiced Sounds from the Glottis. Sounds which have definite pitch 
are called voiced sounds. In the natural larynx, these sounds are generated by 
the vocal chords and drive the vocal tract at the glottis. In an electronic 
analog, the voiced sounds can be generated by a programmable counter (to 
set the frequency) which in turn creates a sine wave of the same frequency. A 
rectified sine wave is a good source for the glottal pulses used in the 
electronic model of a larynx used in the author's approach to speech 
generation. 



the resonant frequency of the filter. Several 
such resonator circuits are then combined as 
in figure 10 to form the vocal tract simu- 
lator. The voicing amplitude control, AV, is 
another digitally controlled resistance similar 
to IC3 of figure 9. 

This gain controlled amplifier configura- 
tion is the means by which the digital 
computer achieves its control of speech 
signal elements. The data of one byte drives 
the switches to set the gain level of the 
amplifier in question. In figures 10, 13 and 
15 of this article, this same variable resis- 
tance under digital control is shown symbol- 
ically as a resistor with a parameter name, Figure 9: Typical Formant 

Resonator Circuit. A 
digitally controlled band 
pass filter can be built 
from four operational 
amplifiers and 8 digitally 
controlled analog switches. 
The filter characteristics 
are set by the choice of 
the resistance and capaci- 
tance elements as well as 
the digital control word. 
The operational amplifier 
IC3 serves as a gain con- 
trolled amplifier in the 
feedback loop, which 
alters the filter resonance. 



^h 



1^ V N S , FILTERED 

AyS~~ OUTPUT 



19 



AC 

SOURCE 
WITH 
DIGITAL 
FREQUENCY 
CONTROL 



f 



AV = 8 BITAMPLITUDE CONTROL 



F3 



Fl 
8 BITS 



F2 
8 BITS 



F3 
8 BITS 



Figure 10: A first approximation of the voice synthesizer can be constructed 
by using three formant filters in series with differing resonance settings all 
controlled by 8 bit digital words. The resistance indicated as AV is an 
operational amplifier circuit (see IC3 of figure 9) with a digital gain control 
input. It is thus a programmable element of gain less than unity, in other 
words the electronically controlled equivalent of a variable resistance. This 
notation of a controlled resistance is used in figures 13 and 15 as well. 



heed 

hid 

head 

had 

hod 

paw 

hood 

who 



Table 1: Steady State English Vowels. The vowel sounds are made by 
adjusting the formant resonances of the human vocal tract to the frequencies 
listed in this table. These figures are approximate, and actual formant 
resonances vary from individual to individual. In a speech synthesizer based 
upon an electronic model of the vocal tract, the formant frequencies are set 
digitally using operational amplifier filters with adjustable resonant peaks. 



F1 


F2 


F3 


250 


2300 


3000 


375 


2150 


2800 


550 


1950 


2600 


700 


1800 


2550 


775 


1100 


2500 


575 


900 


2450 


425 


1000 


2400 


275 


850 


2400 



rather than as an operational amplifier with 
analog switches. 

Generating Vowel Sounds 

The vocal tract circuit as shown thus far 
is sufficient to generate any vowel sound in 
any human language (no porpoise talk, yet). 
Most of the vowels of American English can 
be produced by fixed, steady state formant 
frequencies as given in table 1. A common 
word is given to clearly identify each vowel. 
The formant frequency values shown here 
may occasionally be modified by adjacent 
consonants. 

An alternative way to describe the for- 
mant relationships among the vowels is by 
plotting formant frequencies F1 vs F2 as in 
figure 11. F3 is not shown here because it 
varies only slightly for all vowels (except 
those with very high F2, where it is some- 
what higher). 

The F1-F2 plot provides a convenient 
space in which to study the effects of 
different dialects and different languages. 
For example, in some sections of the United 
States, the vowels in "hod" and "paw" are 
pronounced the same, just above and to the 
right of "paw" on the graph. Also, many 
people from the western states pronounce 
the sounds in "head" and "hid" alike, about 
halfway between the two points plotted for 
these vowels on the graph. 

A few English vowels are characterized by 
rapid sweeps across the formant frequency 



24 00 
2 2 00 - 
2000 - 
I 800 - 
<M I600 



< I400 
9 1200 



1000 
800 



2200 
2000 
I 800 

N 1600 

H 

Z 

< 1400 

a. 

° 1200 

1000 

800 



■ 




- 


■. B«r 


- 


\ N.BUY 


- 


\ boy y. 


; 


y>iow 


- 


"•""hoe 

I 1 1 1 1 1 1 



o 


o 


o 


O 


o 


O 


o 


o 


o 


o 


o 


O 


o 


O 


o 


o 


C\J 


IO 


*■ 


in 


<£ 


r-- 


eo 


0t 






FORMANT 


1 









Figure 11: The Steady State English Vowels. The distinctions between 
various vowel sounds can be illustrated by plotting them on a two 
dimensional graph. The horizontal axis is the formant 1 frequency, the 
vertical axis is the formant 2 frequency. A location for each vowel utterance 
can be determined experimentally by locating the resonance peaks with an 
audio spectrum analyzer. 



Figure 12: English Diphthongs. A diphthong 
is a sound which represents a smooth transi- 
tion from one vowel sound to another 
during an utterance. The time duration of 
the swap from one point to another in 
formant space is typically 150 to 250 ms. 
This graph shows typical starting and ending 
points for several common diphthong 
sounds. 



20 



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Postage and taxes will be added to your 



TITLE 



FIRM 



ADDRESS 



CITY STATE ZI 

*Subject to change without notice 

) AL, AZ, CA, CO. CT. FL, GA, IA, IL, IN, KY, MA, 
MD, Ml, MN, MO, NC, NJ, NM, NY, OH, PA, TN, 
TX, UT, VA, WA, Wl. 



((■) 1976 Texas Instruments Incorporated 
1350 North Central Expressway 
Dallas. Texas 



Texas Instruments 



NCORPORATED 



VOICING 
SOURCE 



ASPIRATION 
SOURCE 



= 8BIT AMPLITUDE CONTROL 




/77 /77 AH=8 BIT AMPLITU 

rfj CONTROL 



Fl F2 

BITS 8 BITS 



Figure 13: Synthesizer with Aspiration Noise Generator. Not all utterances are vowels. By 
adding a digitally controlled noise generator to the circuit of figure 10, it is possible to 
synthesize the consonant sounds known as "stops." In this circuit,. the amplitude versus time 
characteristics of the noise pulse are determined by an 8 bit programmable gain control AH 
(shown symbolically as a resistor). The output of the noise source is mixed with the voicing 
source with the analog sum being routed to the for man t filters. The noise generator is a zener 
diode. 



REL, 
VO 



T 



. F2 
Fl 



100 200 mSEC 



space rather than the relatively stable posi- 
tions of those given in table 1. These sweeps 
are produced by moving the tongue rapidly 
from one position to another during the 
production of that vowel sound. Approx- 
imate traces of the frequency sweeps of 
formants Fl and F2 are shown in figure 12 
for the vowels in "bay," "boy," "buy," 
"hoe" and "how." These sweeps occur in 
150 to 250 ms roughly depending on the 
speaking rate. 



REL.VO 
1 






REL,V0 



r 



j i i_ 



r 



J I L 



"GA" 



RE 

■ 


L VO 

1 


REL VO 

-it 


REL 


V 

1 





\ ^ 


V 


- 










r 
~ i i 


i i i 






1 1 



"PA" 



"TA" 



Figure 14: Stop Consonant Patterns. This figure illustrates 6 different stop 
consonant patterns. The release of the stop closure (start of noise pulse) is at 
the point marked by "Rel" and the beginning of the voicing sounds is marked 
by "VO". Note the typical transition of the vowel formants as the steady 
state is reached. 



Consonant Sounds 

Consonant sounds consist mostly of vari- 
ous pops, hisses and interruptions imposed 
on the vibrating column of air by the actions 
of several components of the vocal tract 
shown in figure 1. We will divide them into 
four classes: 1) stops, 2) liquids, 3) nasals, 
and 4) fricatives and affricates. Considering 
first the basic 'stop consonants,' "p," "t," 
"k," "b," "d" and "g," the air stream is 
closed off, or stopped, momentarily at some 
point along its length, either at the lips, by 
the tongue tip just behind the teeth or by 
the tongue body touching the soft palate 
near the velum. Stopping the air flow briefly 
has the effect of producing a short period of 
silence or near silence, followed by a pulse 
of noise as the burst of air rushes out of the 
narrow opening. 

The shape of the vocal tract with the 
narrow opening at different points deter- 
mines the spectral shape of the noise pulse as 
well as the formant locations when voicing is 
started. Both the noise burst spectrum and 
the rapid sweeps of formant frequency as 
the F1-F2 point moves into position for the 
following vowel are perceived as character- 
istic cues to the location of the tongue as the 
stop closure is released. We need only add a 
digitally controlled noise generator to the 
vocal tract circuit of figure 10 to simulate 
the noise of the burst of air at the closure 
release and we can then generate all the stop 
consonants as well as the vowels. Figure 13 
shows the speech synthesizer with such a 
noise generator added. The breakdown noise 
of a zener diode is amplified by IC1 and 
amplitude is set by the digitally controlled 
resistor AH. IC2 is a mixer amplifier which 
combines the glottal source and aspiration 



22 



VOICING 
SOURCE 



J "h 



AN >• Wr- 



T 



NASAL 
RESONATOR 




Figure 15: The Complete Synthesizer. This diagram shows the organization of a complete synthesizer which includes a wide 
variety of parameters. The voicing frequency and amplitude are set by parameters FV and A V. The noise pulses of stop 
consonants are generated with the programmable gain element AH. The fricative resonator with amplitude AF and frequency 
resonance FF are used to generate fricatives like "s " and "sh. " The normal vowel sounds are generated by control of the formant 
frequencies Fl , F2 and F3, and a nasal resonator with amplitude AN and fixed frequency characteristics is used to add varying 
amounts of nasal sounds. The result of signals processed through the nasal, formant and fricative paths is summed by a final 
operational amplifier and used to drive the output speaker. 



noise at the input to the formant resonators. 

It is important to notice at this point the 
range of different sounds that can be gen- 
erated by small changes in the relative timing 
of the control parameters. The most useful 
of these timing details is the relationship 
between the pulse of aspiration noise and a 
sharp increase in the amplitude of voicing 
(see figure 14). For example, if we set the 
noise generator to come on for a noise pulse 
about 40 ms long and immediately after 
this pulse, F1 sweeps rapidly from 300 up to 
775 Hz and F2 moves from 2000 down to 
1100 Hz, the sound generated will cor- 
respond to moving the tip of the tongue 
down rapidly from the roof of the mouth. 
Observe, however, that the formant output 
is silent after the noise pulse until the 
voicing amplitude is turned up. If voicing is 
turned on before or during a short noise 
burst, the circuit generates the sound "da," 
whereas if the voicing comes on later, after a 
longer burst and during the formant fre- 
quency sweeps, the output sounds like "ta." 
This same timing distinction characterizes 
the sounds "ba" vs "pa" and "ga" vs "ka," 
as well as several other pairs which we will 
explore later. Figure 14 gives the formant 
frequency patterns needed to produce all the 
stop consonants when followed by the vowel 
"ah." When the consonant is followed by a 
different vowel, the formants must move to 
different positions corresponding to that 
vowel. 

The important thing to note about a stop 
transition is that the starting points of the 
frequency sweeps correspond to the point of 



closure in the vocal tract, even though these 
sweeps may be partially silent for the un- 
voiced stops "p," "t" and "k," where the 
voicing amplitude comes on after the sweep 
has begun. 

The second consonant group comprises 
the liquids, "w," "y," "r" and "I." These 
sounds are actually more like vowels than 
any of the other consonants except that the 
timing of formant movements is crucial to 
the liquid quality. "W" and "y" can be 
associated with the vowels "oo" and "ee," 
respectively. The difference is one of timing. 
If the vowel "oo" is immediately followed 
by the vowel "ah," and then the rate of F1 
and F2 transitions is increased, the result 
will sound like "wa." A comparison of the 
resulting traces of F1 and F2 vs time in 
"wa" with the transition pattern for "ba" in 
figure 14 points out a further similarity. The 





Resonator 

Frequency 

(FF) 


Fricative 

Amplitude 

(AF) 


sh, zh 


2500 


.9 


s, z 


5000 


.7 


f, v 


6500 


.4 


th 


8000 


.2 



Table 2: Fricative Spectra. A fricative sound typically consists of a pulse of 
high frequency noise. The various types of fricatives are classified according 
to the spectral profile of the pulse. For the electronic model described here, 
the fricative amplitude and resonator frequency for several sounds are listed 
in this table. 



23 



Product Information 

At the time this article 
goes to press, a synthesizer 
module incorporating several 
detail refinements and im- 
provements over the circuits 
of this article is being de- 
veloped by the author and 
associates. A detailed user's 
guide will be supplied with the 
Computalker module which il- 
lustrates the timing relation- 
ships needed to produce all 
the consonant-vowel and vow- 
el-consonant combinations 
which occur in natural speech. 
This can serve as a reference 
guide for creating your speech 
output software which gener- 
ates the proper control pat- 
terns from text inputs. Write 
to Computalker, 821 Pacific 
St No. 4, Santa Monica CA 
90405 for the latest informa- 
tion on this module. 



direction of movement is basically the same, 
only the rate of transition of "ba" is still 
faster than for "wa." Thus we see the 
parallelism in the acoustic signal due to the 
common factor of lip closeness in the three 
sounds "ua," "wa" and "ba." "Y" can be 
compared with the vowel "ee" in the same 
way, so the difference between "ia" and 
"ya" is only a matter of transition rates. 
Generally, "I" is marked by a brief increase 
of F3, while "r" is indicated by a sharp drop 
in F3, in many cases, almost to the level of 
F2. 

The third group of consonants consists of 
the nasals, "m," "n" and "ng." These are 
very similar to the related voiced stops "b," 
"d" and "g," respectively, except for the 
addition of a fixed "nasal formant." This 
extra formant is most easily generated by an 
additional resonator tuned to approximately 
1400 Hz and having a fairly wide bandwidth. 
It is only necessary to control the amplitude 
of this extra resonator during the "closure" 
period to achieve the nasal quality in the 
synthesizer output. 

The fourth series of consonants to be 
described are the fricatives, "s," "sh," "z," 
"zh," "f," "v" and "th" and the related 
affricates "ch" and "j." The affricates "ch" 
and "j" consist of the patterns for "t" and 
"d" followed immediately by the fricative 
"sh" or "zh," respectively, that is, "ch" = 
"t+sh" and "j" = "d+zh." The sound "zh" is 
otherwise rare in English. An example occurs 
in the word "azure." With the letters "th," 
two different sounds are represented, as 
contained in the words "then" and "thin." 
All the fricatives are characterized by a pulse 
of high frequency noise lasting from 50 to 
150 msec. The first subclassification of 
fricatives is according to voicing amplitude 
during the noise pulse, just as previously 
described for the stop consonants. Thus, 
"s," "sh," "f," "ch" and "th" as in "thin" 
have no voicing during the noise pulse, while 
"z," "zh," "v," "j" and "th" as in "then" 
have high voice amplitude. When a voiceless 
fricative is followed by a vowel, the voicing 
comes on during the formant sweeps to the 
vowel position, just as in the case of the 
voiceless stops. The different fricatives with- 
in each voice group are distinguished by the 
spectral characteristics of the fricative noise 
pulse. This noise signal differs from that 
previously described for the stop bursts in 
that it does not go thru the formant resona- 
tors, but is mixed directly into the output 
after spectral shaping by a single. pole filter. 
Table 2 gives the fricative resonator settings 
needed to produce the various fricative and 
affricate consonants. Fricative noise ampli- 
tude settings are shown on a scale of to 1. 



The Complete Synthesizer 

The system level diagram of a complete 
synthesizer for voice outputs is summarized 
in figure 15. The information contained in. 
this article should be sufficiently complete 
for individual readers to begin experimenting 
with the circuitry needed to produce speech 
outputs. In constructing a synthesizer on 
this model, the result will be a device which 
is controlled in real time by the following 
parameters: 

AV = amplitude of the voicing source, 

8 bits 
FV = frequency of the voicing source, 

8 bits 
AH = amplitude of the aspiration noise 

component, 8 bits 
AN = amplitude of the nasal resonator 

component, 8 bits 
AF = amplitude of the fricative noise 

component, 8 bits 
F1 = frequency of the formant 1 fil- 
ter, 8 bit setting. 
F2 = frequency of the formant 2 fil- 
ter, 8 bit setting. 
F3 = frequency of the formant 3 fil- 
ter, 8 bit setting. 
FF = frequency of fricative resonator 
filter, 8 bit setting. 

This is the basic hardware of a system to 
synthesize sound; in order to complete the 
system, a set of detailed time series for 
settings for these parameters must be deter- 
mined (by a combination of the theory in 
this article and references, plus experiment 
with the hardware). Then, software must be 
written for your own computer to present 
the right time series of settings for each 
sound you want to produce. Commercial 
synthesizers often come with a predefined 
set of "phonemes" which are accessed by an 
appropriate binary code. The problem of 
creating and documenting such a set of 
phonemes is beyond the scope of this 
introductory article, but is well within the 
dollar and time budgets of an 
experimenter." 



BIBLIOGRAPHY 

1. Erman, Lee, ed, IEEE Symposium on Speech 
Recognition, April, 1974, Contributed Papers, 
IEEE Catalog No. 74CH0878-9 AE. 

2. Flanagan, J L, and Rabiner, L R, eds. Speech 
Synthesis, Benchmark Papers in Acoustics, 
Dowden, Hutchinson & Ross, Inc. 1973. 

3. Lehiste, Use, ed. Readings in Acoustic Phonet- 
ics, MIT Press, 1967. 

4. Moschytz, George S, Linear Integrated Net- 
works Design, Van Nostrand, New York, 1975. 



24 




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The Time Has Come to Talk 



Wirt Atmar 

Ai Cybernetic Systems 

PO Box 4691 

University Park NM 88003 



The extent to which art and literature, 
particularly science fiction, affect the future 
course of civilization remains a persistent 
and perplexing question. Must a dream, by 
necessity, occur decades before its realiza- 
tion? Or does the presence of the dream 
itself generate its own reality? Mankind's 
trip to the Moon in 1969 was the dream 
dreamt by Cyrano de Bergerac and Johannes 
Kepler 300 years prior to its enactment. 

And now, we, nurtured by the thousand 
different dreams of the future as portrayed 
in novels and movies, all expect computers 



to be able to talk in the near future. Whether 
we see the computer becoming the benign 
and obedient servant of man or wildly out of 
control, we all tend to see the computer 
becoming more anthropomorphic, more 
humanlike in behavior and form. 

In science fiction two great dreams of the 
future predominate. One is the seemingly 
inevitable first contact with intelligent be- 
ings of an extra terrestrial origin. The second 
is the construction, by our own hands, of an 
alternate embodiment of intelligence in 
machine form. The first dream may well not 




26 



"The time has come, " the Walrus said, 

"To talk of many things: 
Of shoes — and ships — and sealing wax 

Of cabbages — and kings — 
And why the sea is boiling hot — 

And whether pigs have wings. " 



- Lewis Carroll, 1 871 , in 
Through the Looking-Glass. 



occur within the lifetime of our civilization; 
the second would seem to be almost guar- 
anteed within the next 100 years. 

The addition of speech to the computer's 
behavioral repertoire makes the computer no 
more intelligent nor aware than it was 
before. It remains a simple machine. But it 
undeniably takes on a human characteristic 
that it never possessed before. An observer 
finds it impossible not to personify the 
machine with an identity and a distinct 
personality. While the addition of speech is 
only a minor step toward achievement of a 
truly self-organizing, artifically intelligent 
machine, it is a psychologically important 
one. The computer, once it speaks, seems to 
be intelligent. But again, the dream of 
machine produced speech is much older than 
its reality. The ancient Greco-Roman civili- 
zation was fascinated with the idea of deus 
ex machina. Stone gods were often hollowed 
to allow a priest to speak from within, a 
practice that persisted well into the Christian 

era. 

The first known practical realization of 

machine generated speech was accomplished 
in 1791 by a most ingenious engineer, 
Wolfgang von Kempelen, of the Hungarian 
government. Von Kempelen's machine was 
based on a surprisingly detailed under- 
standing of the mechanisms of human 
speech production, but he was not taken 
seriously by his peers due to a previous well 
publicized deception in which he built a 
nearly unbeatable chess playing automaton. 
The "automaton" was unfortunately later 
discovered to actually conceal a legless 
Polish army ex-commander who was a 
master chess player. 

By 1820, a machine was constructed 
which could carry on a normal conversation 
when operated by an exceptionally skilled 
person. Built by Joseph Faber, a Viennese 
professor, the machine was demonstrated in 
London where it sang "God Save the 
Queen." Both the Von Kempelen and Faber 
machines were mechanical analogs of the 
human vocal tract. A bellows was provided 
to simulate the action of lungs; reeds were 



used to simulate the vocal cords, and vari- 
able resonant cavities served to simulate the 
mouth and nasal passages. 

The basic method, modelling the human 
vocal tract, remains to this time the only 
practical method of actually synthesizing 
speech. In the 20th century, such modelling 
is done electronically. The approach was 
first put in electrical analog form by Bell 
Laboratories in the late 1930s. The Bell 
Telephone VODER (Voice Operation 
DEmonstratoR) was initially shown at the 
1939 New York's World Fair where it drew 
large crowds and considerable attention. The 
VODER consisted of a buzz source (similar 
to human vocal cords or mechanical synthesi- 
zers), a hiss source to simulate the rush of 
aspirated air, and a series of frequency filters 
to imitate the three, four, five or six 
preferred frequencies (called formant fre- 
quencies) passed by the resonant cavities 
formed by the mouth, tongue and nose. 

The original VODER was played by 
highly trained operators using a keyboard, 
wrist switches, and pedals at an organ-like 
console. Twenty four telephone operators 
were trained six hours a day over a 12 
month period for the 1939 World's Fair. The 
VODER itself was a full rack in height. 

With the advent of digital computers, 
however, the synthesis of speech has been 
made much easier. All the information 
necessary to repeatedly and reliably generate 
any one speech sound (a "phoneme") can 
now be programmed into the machine. 
Through the proper connection of 
phonemes, a digital computer could be made 
to say words and sentences. 

General American English, the dialect 
spoken in the midwest and southwestern 
parts of the United States, contains 38 
distinct phonemes. These speech sounds can 
be divided into the following classes: 

Pure vowels: produced by a constant 

excitation of the larynx and the 

mouth held in a steady position; eg: 

"e". 

Diphthongs: a transition from one 



27 



(PITCH PERIOD) 



VARIABLE-FILTER 
SYSTEM 



SPECTRAL 
COMPENSATION 




SPEECH 

"output 



DIGITAL 
(TWO LEVEL) 
GAIN CONTROLLED 
AMPLIFIER 



WHITE 
NOISE 
GENERATOR 



FP FZ 

VARIABLE 
POLE/ZERO 
NETWORK 



. I y \ SUMMING 

' V_y AMPLIFIER 



PROGRAMMABLE 
FILTER 



Figure 1: The serial analog speech synthesizer in block diagram form. 



pure vowel to another, thus are not 
always considered as separate pho- 
nemes; "i", "u". 

Fricatives: consonants produced by a 
rush of aspirated air through the vocal 
passages: "f", "s". 

Plosives: explosive bursts of air: "p", 
"k","t". 



Semi-vowels: 
Laterals: "1" 
Nasals: "n", ' 



w 
"r" 

m". 



y 



To produce speech, a separate circuit, or 
combination of circuits, must be provided to 
generate each of the above classes of 
phonemes. 



AFI 



(PITCH PERIOD) 
1 



SPECTRAL 
COMPENSATION 




Among possible realizations of such a 
synthesizer, there are the serial analog and 
parallel analog forms. Figure 1 illustrates a 
block diagram of a serial analog design, and 
figure 2 shows the general organization of a 
parallel analog synthesizer. 

The parallel analog method was the reali- 
zation chosen by Ai Cybernetic Systems for 
its synthesizer module. The parallel realiza- 
tion was chosen because of the low digital 
information transfer rate and the smaller 
number of bits required to control the filters 
which simulate the resonant cavity of the 
vocal tract. 

In the Ai Cybernetic Systems design, the 
rush of aspirated air is generated by the 
noise of a zener diode operated at its knee, 
amplified many times, as shown in figure 3. 
The action of the larynx is simulated by an 
integrated circuit function generator. One or 
both of these circuits is selected to produce 
the excitation necessary to generate any one 
class of phonemes. The actual phoneme 
perceived is determined by the duration of 
the excitation and the selected formant 
filters. Figure 4 shows the typical formant 
filter circuits which are digitally activated by 
analog switches. 

The control of the several analog switches 
is provided by a read only memory which is 
addressed by the ASCII bit patterns identi- 
fied in table 1. 

No hard and fast rules exist in the design 
of the circuitry to generate a phoneme. In 
fact, small changes in component values can 
often make large differences in the phoneme 
which is actually heard. Because no set rules 
exist, a steady stream of listeners must 
parade before the machine while it is being 
designed in order to determine which 
phoneme the synthesizer is really saying. 
The phenomenon of "tired ears" rapidly sets 
in; and a person will begin, after a bit, 
hearing any one speech sound as a whole 
array of possible phonemes. Suggestion, on 
the other hand, is an ever obtuse enemy to 
the designer. Surprisingly, almost any speech 
sound can be suggested to sound like a great 



.SPEECH 
' OUTPUT 



WHITE- 
NOISE 
GENERATOR 



Figure 2: The parallel ana- 
log speech synthesizer in 
block diagram form. 



28 



+ 12 



WHITE-NOISE 
GENERATOR 



WHITE NOISE AMPLITUDE 
AN 




RESISTANCE 
DETERMINED 
BY 
FACTORY 



VOICE 
GENERATOR 



PITCH PERIOD 
CONTROL 



I I 

I I 

DIGITALLY CONTROLLED 
ANALOG SWITCH 



number of alternate phonemes, especially 
after 20 to 30 minutes of intense listening. 

Once the design is experimentally deter- 
mined, careful procedures must be followed 
to insure that when the circuit is duplicated, 
it produces each phoneme properly. This 
means precision components must be used, 
as small changes in values can make the 
difference between moderately distinct 
speech and a fairly mushy speech. 

Analog simulation of the vocal tract is the 
only method of true speech synthesis 



known. A popular alternate method of 
speech production (actually, reproduction) 
is the storage of digitized speech in a ROM. 
When the stored information is clocked out 
of the ROM at the proper rate and smoothed 
by a low pass filter, the generated speech can 
be quite clear and distinct. But it is impor- 
tant to note that this is not synthesized 
speech. In effect, this method is no different 
than any other method of recording speech. 
Yet, the method does have the advantage of 
producing readily understood words by a 



Figure 3: The excitation 
sources of the Ai Cyber- 
netic Systems Model 1000 
Speech Synthesizer. The 
rush of air through the 
vocal passages is simulated 
in the upper branch while 
the action of the larynx is 
simulated in the lower 
branch. 



Figure 4: The parallel fil- 
ter network of the Model 
WOO. The filter fre- 
quencies and quality fac- 
tors chosen depend on the 
number of filters used to 
divide the voice frequency 
spectrum. Ideally, the cen- 
ter frequencies of the 
filters should lie some- 
where near the commonly 
occurring formant 
frequencies. 



FROM 

EXCITATION 

SOURCES 




AF 
FORMANT I 
AMPLITUDE 



AF2 
FORMANT 2 
AMPLITUDE 



FORMANT FILTER NO. I 

*Ht 



-)h 



1 r 




, FORMANT FILTER NO. 2 




IK 
-vw- 



0.5 fj. F 



^h 



¥ 



SPEECH 
OUTPUT 



I I 






DIGITALLY CONTROLLED 
ANALOG SWITCH 



29 




Photo 1 : The Ai Cybernetic Systems Model 1000 Speech Synthesizer. The 
synthesizer is primarily an analog circuit controlled digitally. Ten active filters 
composed of 1 5 operational amplifiers are mounted in the upper left corner 
of the board. Directly beneath these resonant-cavity simulating filters are the 
vocal excitation circuits. The right half of the board is composed of the 
ASCII character decoding circuits and phoneme memories. Four 32 x 8 
ROMs control the 16 analog switches to select the proper combination of 
circuits to generate any one phoneme. A device-busy flag is returned for the 
duration of the phoneme. 

computer or calculator. However, the vocab- 
ulary is totally predefined and must remain 
small due to the high cost of storing this 
kind of generated speech. Moreover, the 
repertoire of this kind of speech is limited to 
the person who initially spoke the recorded 
words. 

Synthetic speech, on the other hand, is 
generally not as clear and distinct. The 
proper transitions from phoneme to pho- 
neme, the automatic emphasis given to 
leading or terminating consonants, and the 
intonation of a rhythm in speech which is 
associated with a word's importance or 
placement, are all facets of human speech 
which are difficult to properly recreate in 
machine produced speech. The determina- 
tion of accurate rules to account for these 
factors has been the subject of active and 
intense research at centers here, and in 
Europe and Japan, including Bell Telephone 
Laboratories, the Haskins Laboratories of 
New York, the Royal Institute of Tech- 
nology in Sweden, and the Musashino Elec- 
trical Communication Laboratory in Tokyo. 
On the whole, totally satisfactory rules have 
not yet been worked out although a great 
deal of progress has been made in the last 20 
years. Machines which do incorporate the 
known rules quickly become elaborate and 
expensive (in the tens of thousands of 
dollars). 



Simplified speech rules can be incor- 
porated in a much smaller machine, but the 
burden of intelligibility now falls upon the 
listener. The produced speech is not natural 
speech. It sounds for all the world like the 
speech produced by the robots of 1950s 
grade B science fiction movies. But it is 
intelligible and it is quickly learned. Because 
the machine pronounces every phoneme in 
the same fashion each time it occurs, a 
listener quickly gains a feeling for the 
speech. The process is not unlike learning to 
listen to a newly-arrived foreigner who 
possesses a strong accent. The fashion by 
which he mispronounces the English 
phonemes is quickly learned and intel- 
ligibility increases rapidly. The difference 
with synthetic speech is that the speech is 
truly an alien form of speech, not often 
heard before by many of us. 

As to the naturalness of synthetic speech, 
M D Mcllroy of Bell Telephone Labs wrote 
this in 1974 [in "Synthetic English Speech 
by Rule," Computer Science Technical Re- 
port No. 14, Bell Telephone Laboratories] : 



The Computer Science Center at this 
laboratory has experimented with an 
inexpensive speech synthesizer [pre- 
sumed to be the Votrax] as a regular 
output device in a general purpose 
computing system. Our intention was 
not to do speech research or to create 
artificial speech as an end in itself. In 
the present state of the art, those goals 
require much more elaborate facilities 
than we have at our disposal. 

We wished to see what uses might 
evolve when speech became available 
more or less on a par with printed out- 
put. For this goal, "naturalness" was 
not a prerequisite, any more than it is 
for printed output. Most computers 
still print mainly in upper case, are 
incapable of printing mathematical 
notation, and normally produce 
cryptic codes or tabular stuff that 
require considerable indulgence to be 
understood. Since printed gobbledy- 
gook is so widely accepted from com- 
puters — and fed into them, witness 
any manufacturer's operating system 
manual — we suspected that spoken 
gobbledygook might be quite passable, 
too, except for one severe difficulty: 
Being ephemeral, sounds must be 
understood at first hearing. As it turns 
out, long speeches are hard to under- 
stand, as are extremely short utter- 
ances of very simple words out of 
context. But given a little familiarity 



30 



r 



"\ 




MICROPROCESSOR 

VOLUME 2 



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Send my 
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Name 



Title 



V 



Company 
Address — 
City 



State 



-ZIP Code 



Vowels: 



with the machine's "accent", one finds 
short sentences to be quite intelligible. 

The phonemes generated by the Model 
1000 synthesizer appear in table 1. Each 
phoneme has been assigned an ASCII charac- 
ter to represent its particular sound. The 
assignment was done in the most intuitive 
manner possible; the consonants are gener- 
ally the consonants as they appear on the 
keyboard, but there are many more vowels 
than a, e, i, o and u. Non-alphanumeric 
characters were chosen to represent the 
remaining vowels and consonants in such a 
manner that they could be easily associated 
with their sound. As examples of this, the 
number symbol, "#" is used to signify the 
vowel er as in number, "&" for the vowel ae 
as in and "(" for ah and ")" for aw 



Table 1: List of Phonemes. 
Phoneme ASCII Symbol 



Usage 





a 


A 


pace, bay 




ae 


& 


and, Altair 




ah 


( 


father, all 




aw 


) 


bought, robot 




e 


E 


see, harmony 




eh 


' 


excessive, ten 




er 
i 


# 
I 


number, bird 
hit, six 




o 





Mexico, over 




oo 


U 


too, sue 




uh 


! 


the, computer 




A 


t 


putt, up 


Semi-Vowels: 










w 


W 


water, wind 




y 


Y 


yaw, yacht 


Plosives: 










p 


P 


pop, deep 




k 


K 


computer, Atlantic 




t 


T 


top, pot 




b 


B 


boy, bird 




d 


D 


dog, died 




g 


G 


go, great 


Fricatives: 










f 


F 


puff, food 




h 


H 


how, had 




s 


S 


saw, miss 




V 


V 


David, vow 




sh 


/ 


slash, shoot 




th 


+ 


thaw. Earth 




z 


z 


zero, is 


Liquids: 










1 


L 


low, all 




r 


R 


row, round 


Nasals: 










m 


M 


miss, am 




n 


N 


now, nine 


Others: 










Glottal Stop 




The pause associated 
with aspiration 




Draw Bar 


- 


An extended vowel 
with decay 




Pause 


(space) 


Normal word spacing 



representing the position of the tongue when 
these vowels are spoken, "!" for the sharp 
sound of uh, "+" for the fricative consonant 
th as in thaw, and "/" for the sh in s\ash. 

The Model 1 000 accepts a string of ASCI I 
characters as if it were a normal printing 
device. Read only memories on the board 
convert the incoming ASCII symbol into 
specific control information which in turn 
determines the vocal source, duration and 
frequency content of the spoken phoneme. 
Less than 50 bytes of machine code or 8 
lines of the typical BASIC are all that is 
required to generate a subroutine to accept a 
string of characters and output it character- 
by-character to the synthesizer. 

For example, to write the phrase "I am a 
talking robot" on a printer or display periph- 
eral, an ASCII character string is set up and 
sent to the output device. In BASIC, if C$ is 
the argument of the output subroutine, the 
setup would be: 

C$ = "I AM A TALKING ROBOT." 

To have the synthesizer say the same phrase, 
the setup for the phonetic output routine 
with argument P$ might be: 

P$ = "&IE AM AET). .KEN- RO.B). .T" 

(The ASCII symbols are taken from table 1.) 
The long vowels I and A occur in this 
passage. As a rule, most of the long vowels 
are not really vowels at all but rather 
diphthongs composed of a sequence of pure 
vowels. Pronounce out loud each of the 
phonemes in the phrase above, referring to 
table 1 as necessary. Remember that each 
phoneme has only one specific sound. Play- 
ing the part of a synthesizer yourself, you 
will find that you can say any English word 
with the phonemes of table 1. 

Programming the Model 1000 synthesizer 
is easy once you actually begin to listen to 
what you say and learn to rely less on how a 
word is written. English is a hodge podge of 
languages and carries with it all the alternate 
symbolisms of the pronunciations of its root 
languages. Purely phonetic languages such as 
the Polynesian languages of Samoa or Tonga 
could be made to be spoken almost as they 
are written. This is unfortunately not true of 
English; homonyms such as "won" and 
"one" and "two", "too" and "to" abound. 

Generally, only one phonetic spelling 
exists for any one word regardless of the 
number of alternate written spellings. It 
becomes important to identify the sounds 
that you actually are saying when a word is 
pronounced. The word "one" is phoneti- 
cized using the phonemes of table 1 as WIN 
in similarity to the word "won"; "two" is 
programmed as TOU- more as if it were the 



32 



written word "too". For most Americans, 
there is no difference in the way these words 
are pronounced. 

Proceeding in the same fashion, the 
remaining numbers up to ten are typed in as: 

T+#E- FO#- F&IE..V SI..KZ 
S'-VIN AE..T N&IEN T'N 

Again, pronounce these phonetic spellings to 
yourself. As you will discover, phonetic 
spellings are quickly deduced and learned. 

In a very short period of time, it becomes 
possible to make the machine say anything. 
At that point, conversational computing 
takes on a whole new meaning. Interactive 
computing will never again be the same once 
your computer has actually spoken to you." 



BIBLIOGRAPHY 

Speech Synthesis, Benchmark Papers In Acous- 
tics, 1973. J L Flanagan and L R Rabiner, eds. 
Dowden, Hutchinson and Ross, Stroudsburg 
PA. A collection of the best papers on speech 
synthesis over the past 35 years. 
"Synthetic Voices for Computers," 1970. J L 
Flanagan, C H Coker, L R Rabiner, R W 
Schater, N Umeda in IEEE Spectrum 7:22-45. 
An authoritative overview of the speech synthe- 
sis procedure. 

"The Synthesis of Speech," 1972. J L Flana- 
gan, Scientific American 226:48-58. A simpli- 
fied rework of the IEEE Spectrum article 
above. 

IEEE 1974 Speech Recognition, Proceedings, 
1974. L Erman, ed. IEEE, NY. A bit too 
technical for a first introduction but a good 
measure of where things are going. 



COMMERCIAL PRODUCTS 

At the present time, two speech synthesizers 
are both commercially available and affordable by 
the hobbyist. One is the Votrax produced by: 

Vocal Interface Division 

Federal Screw Works 

500 Stephenson Dr 

Troy Ml 48084 

Price, approximately $2,000 

Interfacing: Parallel or Serial (RS-232) 

The second is the Model 1000 manufactured by: 

Ai Cybernetic Systems 

PO Box 4691 

University Park NM 88003 

Price, $425 

Interfacing: Electrically and mechanically 
compatible with Altair/IMSAI/ 
Poly-88 bus structure. 

Either company will be pleased to provide 
literature free of charge. A demonstration tape is 
available from Ai Cybernetic Systems for $5 and a 
complete programming guide, theory of operation 
manual and phonetic glossary is available for 
$2.50. 




33 ' 






Video Terminal Interface: This is 
one almost every owner of an Altair- 
compatible computer needs. There 
have been problems getting parts for 
this one (the people with the other 
Video board have had the same 
problem, since they use the same 
hard-to-get chip), but deliveries are 
improving. By the way, our video 
board has GRAPHICS as well as 
an 8 bit parallel key board input 
port, so compare before you buy. 
$185.00 - $210.00 kit depending on 
whether 32 or 64 characters per line. 

Poly I/O: With this one you will 
save a lot of time in making proto- 
type circuits. I/O port address is 
selectable with dip switch and fully 
buffered inputs and outputs. $55 kit. 

Analog Interface: Good for interfac- 
ing your computer to an analog 
world. Ten bits of resolution in and 
out. $145.00 for one channel and 
$195.00 for two channels (kit). 

Ask about how to get a free POLY 
I/O or ANALOG Board. 

Watch for our new products. Next 
time they will be on the shelf before 
we advertise. 

Have you heard about the POLY-88? 
We don't have the space here to 
describe all the features.See it at 
your local computer store (except 
(or MITS dealers, though some do 
carry our other products). This might 
be the system you're looking for. 

Support your local computer store. 

All prices and specifications subject to change 
without notice. Prices are U.S.A. only. Calif, 
residents add 6% sales tax. Add 5% shipping, 
handling, and insurance. Bank Americard and 
Mastercharge accepted. 

PoIyMorphic 
Systems 

737 S. Kellogg, Goleta, Calif. 93017 
(805) 967-2351 




Photo J: The Z80 microprocessor evaluation board. 



Microprocessor Update: ZllOg Z80 



Burt Hashizume 
PO Box 172 
Placentia CA 92670 



One feature of the Z80 
not found in other 8 bit 
microprocessors is a built 
in dynamic MOS memory 
refresh algorithm which 
employs unused memory 
cycles to do hidden (from 
software timing) refresh 
operations. 



Zilog, a fairly new company in Los Altos 
CA, has been sampling an 8 bit micropro- 
cessor, the Z80, since early this year. The 
Z80 is a "third generation," single chip, 
NMOS microprocessor, which is completely 
software compatible with Intel's 8080A. Its 
158 instructions include the 8080A's 78 
instructions as a subset. Because the 8080A 
is probably the most widely used 8 bit 
microprocessor on the market today and 
because of the Z80's upward software com- 
patibility, this article evaluates the Z80 in 
comparison to the 8080A. 

Physical and Electrical 
Characteristics 

The Z80 processor is packaged in the 
standard 40 pin dual in line package; how- 



ever, even though the Z80 is software 
compatible with the 8080A, it is most 
definitely not pin compatible. (See figure 1 
and table 1 for pinout definitions.) There are 
numerous differences between the two pro- 
cessors as far as electrical characteristics are 
concerned. 

The 8080A requires three voltage levels, 
+12, +5, and —5 V. A high voltage two phase 
clock is also required. Maximum speed is a 
480 ns clock period. Finally, some sort of 
system controller is needed to separate the 
system control signals from the data bus. 
This all makes for a fairly complex system 
design around the 8080A. 

On the other hand, it is very easy to 
design a system around the Z80. It requires 
only a single +5 V power supply because the 



34 



technology used is of the same type used by 
Motorola in its 6800 microprocessor, which 
also requires a single 5 V power supply. The 
Z80 requires a single phase 5 V clock. 
Maximum frequency is 2.5 MHz for a 400 ns 
clock period. System control signals, such as 
memory read and write, have separate pins 
from the processor and are not time shared 
with the data bus. An additional feature not 
found on any other microprocessor at the 
time of this writing is the capability to 
refresh dynamic memory. 

Because the Z80 is upward software 
compatible with the 8080A, the internal 
architectures are similar. (See the register 
configuration in figure 2.) Both have 16 bit 
program counters and stack pointers as well 
as a register array of six general purpose 
registers, (B, C, D, E, H and L), an accumu- 
lator (A), and a flag register (F). 

The Z80 has numerous additional 
characteristics. It has an additional duplicate 
register array consisting of 8 registers (A', F', 
B', C, D', E', H' and L'). These can be 
switched with the primary register array for 
fast interrupt processing. There are also two 
16 bit index registers (IX and IY) for 
increased addressing capability and easier 
data manipulation. An 8 bit interrupt vector 
register (I) expands the capability and in- 
creases the power and speed of interrupt 
handling by the processor. Finally, an 8 bit 
memory refresh register (R) automatically 
increments after every instruction fetch and 
refreshes memory while the processor is not 
using the bus. Thus the execution time of 
the system is not increased due to refresh 
overhead. 

Software 

Now that we have seen the hardware 
aspects of the Z80 and how it compares to 
the 8080A, let's take a look at its instruction 
set. The fact that the Z80 has 158 instruc- 
tions versus the 8080A's 78 gives only a 
small indication of its technological super- 
iority in this area. The instruction set can be 
broken up into two aspects, addressing 
modes and instruction groups. 

Since the Z80 is software compatible 
with 8080A, it necessarily has the same 
addressing modes as the 8080A. The modes 
in common are register addressing, register 
indirect addressing, direct addressing, and 
immediate addressing. 



SYSTEM 
CONTROL < 



CPU 
CONTROL < 



"I 

MREQ 
IORQ 
RD 

WR 

RFSH 

Halt 
wait 
IFf 

NMl 



CPU 
BUS 
CONTROL 



J BUSRO 
1 BUSAK 



+ 5V 
GND 



27 


Z-80CPU 


30 , 




31 . 


. I9 


32 . 


20 


33 , 


21 


34 . 


22 


35 




36 , 


j 28 


37 r 




38 t 


18 


39 r 




40 r 


24 . 


1 r 




2 t 


16 


3 r 


17 


4 . 




5 


26 




25 


. I4 ■ 


23 


. ' 5 . 




. I2 . 




. e , 


6 


, 7 , 


1 1 


, 9 . 


29 


. I0 » 




. I3 . 







*0 

*l 

*3 



*6 
*7 
A 8 



A| 4 
A|5 



DO 
°l 
°2 
°3 
°4 
°5 
°6 
°7 



> ADDRESS BUS 



>DATA BUS 



Figure I: Pin configuration of the 180 processor. Of particular note to 
custom hardware hackers is the "M] "line which gives users the possibility of 
identifying instruction cycles. 



Table 1 : Signal list for the 180 processor. This table lists each active pin of 
the Z80 with a short explanation of its purpose. 



A 0-A-|5 
(Address Bus) 



D -D 7 
(Data Bus) 



M 1 

(Machine Cycle one) 



MREQ 

(Memory Request) 



IORQ 

(Input/Output Request) 



Tri-state output, active high. An— A15 constitute a 16 bit 
address bus. The address bus provides the address for 
memory (up to 64 K bytes) data exchanges and for IO 
device data exchanges. IO addressing uses Xhe 8 lower 
address bits to allow the user to directly select up to 256 
input or 256 output ports. An. is the least significant 
address bit. During refresh time, the lower 7 bits contain a 
valid refresh address. 

Tri-state input and output, active high. Do— D7 constitute 
an 8 bit bidirectional data bus. The data bus is used for 
data exchanges with memory and IO devices. 

Output, active low. Mi indicates that the current machine 
cycle is the OP code fetch cycle of an instruction 
execution. 

Tri-state output, active low. The memory request signal 
indicates that the address bus holds a valid address for a 
memory read or memory write operation. 

Tri-state output, active low. The IORQ signal indicates 
that the lower half of the address bus hold s a va lid 10 
address for a IO read or write operation. An IORQ signal 



35 



Table 1 (continued). 



RD 

(Memory Read) 



WR 

(Memory Write) 



RFSH 
(Refresh) 



HALT 
(Halt state) 



WAIT 
(Wait) 



INT 

(Interrupt Request) 



NMI 

(Non Maskable 

Interrupt) 



RESET 



BUSRQ 
(Bus Request) 



BUSAK 

(Bus Acknowledge 



is also generated when an interrupt is being acknowledged 
to indicate that an interrupt response vector can be placed 
on the data bus. Interrupt Acknowledge operations occur 
during M-| time while 10 operations never occur during 
M-] time. 

Tri-state output, active low. RD indicates that the 
processor wants to read data from memory or an 10 
device. The addressed IO device or memory should use 
this signal to gate data onto the processor data bus. 

Tri-state output, active low. WR indicates that the 
processor data bus holds valid data to be stored in the 
addressed memory or 10 device. 



Output, active low. RFSH indicates that the lower 7 bits 
of the address bus contain a refre sh address for dynamic 
memories and the current MREQ signal should be used to 
do a refresh read to all dynamic memories. 



Output, active low. HALT indicates that the processor has 
executed a HALT software instruction and is awaiting 
either a non maskable or a maskable interrupt (with the 
mask enabled) before operation can resume. While halted, 
the processor executes NOPs to maintain memory refresh 
activity. 



Input, active low. WAIT indicates to the Z80 processor 
that the addressed memory or 10 devices are not ready 
for a data transfer. The processor -continues to enter wait 
states for as long as this signal is active. This signal allows 
memory or 10 devices of any speed to be synchronized to 
the processor. 

Input, active low. The Interrupt Request signal is 
generated by 10 devices. A request will be honored at the 
end of the current instruction if the internal software 
control led inte rrupt enable flip flop (IFF) is enabled and 
if the BUSRQ signal is not active. When the pr ocessor 
accepts the interrupt, an acknowledge signal (IORQ 
during Mi time) is sent out at the beginning of the next 
instruction cycle. The processor can respond to an 
interrupt in three different modes that are described in 
detail in the Zilog documentation. 

Input, active low. The non mas kable interrupt request line 
has a higher priority than INT and is always recognized at 
the end of the current instruction, i ndep endent of the 
status of the interrupt enable flip flop. NMI automatically 
forces the Z80 processor to restart to location 0066 
hexadecimal. The program counter is automatically saved 
in the external stack so that the user can return to the 
program that was interrupted. 



Input, active low. RESET forces the program counter to 
zero and initializes the processor. The processor ini- 
tialization includes: 

1 ) Disable the interrupt enable flip flop 

2) Set Register 1 = 00 

3) Set Register R = 00 

During reset time, the address bus and data bus go to a 
high impedance state and all control output signals go to 
the inactive state. 

Input, active low. The bus request signal is used to request 
the processor address bus, data bus and tri-state output 
control signals to go to a high impedance sta te so th at 
other devices can control these buses. When BUSRQ is 
activated, the processor will set these buses to a high 
impedance state as soon as the current processor machine 
cycle is terminated. 

Output, active low. Bus acknowledge is used to indicate 
to the requesting device that the processor address bus, 
data bus and tri-state control bus signals have been set to 
their high impedance state and the external device can 
now control these signals. 



• Register addressing. The opcode itself 
specifies a register or register pair in 
which the data is contained. An 
example would be to load the data in 
register B into register D. 

• Register indirect addressing. The 
opcode specifies a register pair which 
contains a 16 bit address. This address 
points to the data in memory or is an 
address to be loaded into the program 
counter (PC). An example would be to 
load the accumulator with data in 
memory pointed to by the HL register 
pair. 

• Direct addressing. The opcode is fol- 
lowed by two bytes of operand. These 
two bytes are either a 16 bit address 
pointing to data in memory or a 16 bit 
address to be loaded into the PC. For 
example, in a jump instruction, the 
two bytes indicate an address to which 
program control is transferred. 

• Immediate addressing. The opcode is 
followed by one or two bytes of 
operand. This operand is the data itself 
to be used. An example is load 
accumulator immediate which moves 
an 8 bit operand into the accumulator. 

To these addressing modes, the Z80 has 
added three more powerful modes. These are 
indexed addressing, relative addressing, and 
bit addressing. The first two are somewhat 
similar to index and relative addressing in 
the Motorola 6800 microprocessor. 

• Indexed addressing. The opcode is 
followed by an 8 bit displacement. 
This displacement is a signed two's 
complement number to be added to 
the contents of one of the two index 
registers. The result is a 16 bit effec- 
tive address. The contents of the index 
register are unchanged. 

• Relative addressing. The opcode is 
followed by an 8 bit signed two's 
complement number. The number is 
added to the contents of the program 
counter and the result placed back in 
the PC. This results in being able to 
execute program jumps within a range 
of +129 to -126 bytes using only a 
two byte instruction. Since most pro- 
grams have a lot of jumps to locations 
relatively close to current locations, 
using relative addressing will signi- 
ficantly reduce program size. Another 
advantage is the ability to write re- 
locatable code using relative address- 
ing. 

• Bit addressing. Three bits in the 
opcode itself specify one of eight bits 
in a byte to be addressed. This byte 



could be the contents of a register or 
of a memory location. An example 
would be to set bit 6 in memory 
pointed to by index register, IX, dis- 
placed by —20. 

The Z80 instruction set's increase of 80 
instructions over the 8080A's didn't come 
from just increasing the number of address- 
ing modes. There are instructions which 
don't exist in any other microprocessor. The 
instruction set will be broken up into groups 
by their function. 

Load and Exchange Instructions 

This group includes all the instructions 
that move data to and from registers, such as 
load B from D, load C from memory, store 
HL into memory, push IX into stack, and 
exchange AF with A'F'. The 8080A has 
most of the same instructions. 

Block Transfer and Search 
Instructions 

This group has several useful and unique 
instructions. The load and increment instruc- 
tion moves one byte of data from memory 
pointed to by HL to another memory 
location pointed to by DE. Both register 
pairs are automatically incremented and the 
byte counter, BC, is decremented. This 
instruction is extremely valuable in moving 
blocks of data around. 

Another instruction repeats the load and 
increment instruction automatically until 
the byte counter reaches zero. Thus, in one 
instruction, a block of data, up to 64 K 
bytes in length, can be moved anywhere in 
memory. Each byte of data transferred 
requires only 8.4 jus. 

In the compare and increment instruc- 
tion, the contents of the accumulator are 
compared with that of memory pointed to 
by HL. The appropriate flag bits are set, HL 
is automatically incremented, and the byte 
counter is decremented. 

The instruction compare, increment, and 
repeat repeats the above instruction until 
either a match is found or the counter 
reaches zero. 

The 8080A has no analogy to these 
instructions. It would have to execute three 
to ten separate instructions to achieve the 
same result. The number of bytes would be 
several times larger and the execution time 
would be several times longer. 

Arithmetic and Logical Instructions 

These instructions include all the adds 
and subtracts, increments, compares, ex- 
clusive-ors, etc. What the Z80 has added to 



MAIN REG SET 
A 



ALTERNATE REG SET 
A 



ACCUMULATOR 
A 


FLAGS 

F 


ACCUMULATOR 
A' 


FLAGS 
F' 


B 


C 


B' 


C 


D 


E 


D' 


E' 


H 


L 


H' 


L' 



the 8080A instructions is the indexed ad- 
dressing mode and double precision add with 
carry and subtract with carry. 

Rotate and Shift Instructions 

Here the Z80 has taken the four 8080A 
rotate accumulator instructions and in- 
creased the possible addressing modes as well 
as included logical shifts and arithmetic 
shifts. On top of this there are a couple of 
rotate digit instructions. With these a digit (4 
bits) can be rotated with two digits in a 
memory location, which is great for BCD 
arithmetic. 

Bit Manipulation Instructions 

There are three basic operations, test bit, 
set bit, and reset bit. With the various 
addressing modes, a powerful group of in- 
structions is generated. For instance, if 
several memory locations are used for 10 
devices, status bits can be individually tested 
and control bits individually set or reset. The 
8080A (nor any other 8 bit microprocessor) 
has no such capability to manipulate bits. 

Jump, Call, and Return 

Both the 8080A and Z80 have numerous 
conditional and unconditional jumps, calls, 
and returns. In addition, the Z80 has several 
jump relative instructions using relative ad- 
dressing. One of special interest decrements 
the B register, and jumps relative if B is not 
zero. This is especially useful in program 
loop control; it would take the 8080A two 
instructions to perform the same task. 

Input/Output Instructions 

The 8080A has two 10 instructions, input 
and output to and from the accumulator. 
The device address is in the second byte of 
the instruction, which means that each 



GENERAL 
> PURPOSE 
REGISTERS 



INTERRUPT 

VECTOR 

1 


MEMORY 
REFRESH 
R 


INDEX REGISTER IX 


INDEX REGISTER IY 


STACK POINTER SP 


PROGRAM COUNTER PC 



SPECIAL 
> PURPOSE 
REGISTERS 



Figure 2: Programmable 
registers of the Z80. Con- 
siderable improvement 
over the 8080 design is 
found in the alternate 
register set, and the addi- 
tion of two index registers, 
interrupt vector and mem- 
ory refresh registers. 



The Z80 should be a nat- 
ural for string manipula- 
tion software with its pair 
of full 16 bit index 
registers and powerful 
multi-byte operations such 
as block move, memory 
search and block 10 in- 
structions. 



37 



In addition to expanding 
operations upward to the 
level of blocks, the Z80 
refines its addressing 
downward to the bit level 
with a group of bit mani- 
pulation instructions 
which are quite unique. 



The Z80 simplifies the 
hardware required to im- 
plement a system as com- 
pared to the original 8080 
design. Aside from the in- 
struction enhancements, 
here is a way to get an 
8080 instruction set with 
the ease of interfacing un- 
til now only available (in 8 
bits) with processors like 
the 6800 and 6502. 



For more information on 
the Z80 CPU and other Z80 
parts contact Zilog Inc. 170 
State St, Ste 260A, Los Altos 
CA 94022, (415) 941-5055." 



device must have its own IO routine. One 
standard routine can't be used in common 
because each device has a different address 
and therefore different instruction. The Z80 
has resolved this by including IO instructions 
that use the C register to contain the IO 
device address. Therefore one IO routine can 
be used with the device address placed in 
register C before entering the routine. Also 
instead of being restricted in inputting or 
outputting to and from the accumulator 
only, any register can be used. 

If this isn't enough, the Z80 has eight 
block transfer IO instructions which are 
similar to the memory block transfer instruc- 
tions. HL is the only memory pointer, C is 
the device pointer, and B is the byte 
counter. Therefore, an IO block transfer can 
handle up to 256 bytes. Essentially these 
commands are a processor implementation 
of direct memory access (DMA), invoked by 
a software sequence. 

Miscellaneous Features 

These instructions include no-operation, 
halt, enable and disable interrupts, decimal 
adjust accumulator, set carry, and com- 
plement carry. The Z80 can also select one 
of three interrupt modes. 

Interrupts on the Z80 

The 8080A has one input for interrupts; 
the Z80 has two. One is a nonmaskable 
interrupt (similar to the Motorola 6800 or 
MOS Technology 6502) which cannot be 
disabled by the software. The other is a 
maskable interrupt which can be selectively 
enabled or disabled by the program. The 
maskable interrupt is analogous to the single 
8080A interrupt. 

A nonmaskable interrupt will be accepted 
at all times by the Z80 processor. When one 
occurs, the processor will execute a restart 
to hexadecimal location 0066. The non- 
maskable interrupt is used for very impor- 
tant functions that must be serviced imme- 
diately, such as a power failure routine. 

The Z80 has three programmable modes 
for processor response to a maskable inter- 
rupt. There are three instructions that will 
select these three modes. 

Mode is identical to the 8080A single 
interrupt response mode. The interrupting 
device places an instruction on the data bus, 
and the processor executes it. The instruc- 
tion will often be a restart. This mode is also 
the default mode for the Z80 upon a reset. 

In mode 1, the processor will respond to 
an interrupt by executing a restart to loca- 
tion 0056. The response in this mode is 
similar to the response to a nonmaskable 
interrupt except for the restart location. 



In mode 2, a table of 16 bit starting 
addresses for every interrupt routine must be 
maintained. This table can be anywhere in 
memory. When an interrupt is accepted, a 16 
bit address is formed from the contents of 
the 8 bit I register and the 8 bits on the data 
bus. The I register contains the upper 8 bits 
of the address and the 8 bit data on the data 
bus from the peripheral device constitutes 
the lower 8 bits of the address. This 16 bit 
address points to a location in the interrupt 
vector table. The processor fetches the 16 
bit address found at the selected table 
location (in two bytes) and loads the pro- 
gram counter with its value. This whole 
process takes 19 clock periods, or just 7.6 
us. 

The peripheral devices in the Z80 micro- 
computer family all have daisy chain inter- 
rupt structures. They automatically supply a 
programmed vector to the processor during 
interrupt acknowledge. Only the highest 
priority device interrupting the processor 
sees the interrupt acknowledge because of 
the daisy chain structure. With these devices, 
IO interfacing becomes quite a simple task, 
and is as powerful as the IO techniques used 
in many minicomputers. 

Conclusion 

What does the Z80 have going for it? It's 
easy to interface; one chip does the job of 
several 8080A family chips. It's as easy, if 
not easier, to design an entire system around 
than any other microprocessor on the mar- 
ket today, and the Z80 is software com- 
patible with the 8080A, the most widely 
used and known 8 bit microprocessor. Its 
instruction set is much more powerful than 
the 8080A's or any other 8 bit micropro- 
cessor's instruction set. 

Is there anything negative about the Z80? 
As of this writing (March), it is not yet in 
production and therefore not readily avail- 
able to the personal computing ex- 
perimenter. The price tag for unit samples is 
$200, but there are numerous price breaks 
with larger quantities. For instance, the price 
is $80 for quantities of 25 - 99. This is still 
more expensive, however, than either the 
8080A, 6800 or 6502, and is about the same 
as 16 bit microprocessors. 

The result is a tradeoff of cost versus 
performance. Much of the cost difference 
relative to other 8 bit processors is made up 
by the Z80's better memory utilization and 
(with respect to the 8080A) by the fact that 
fewer parts are needed to get a minimum 
system going. Although the Z80 processor is 
priced higher than the 8080A, when the cost 
of all the support devices the 8080A requires 
are included, the costs are comparable." 



38 




TDL IS PROUD TO ANNOUNCE THE REVOLUTIONARY Z-80 CPU CARD, 
AN ALTAIR/IMSAI COMPATIBLE CPU CARD FEATURING THE POWERFUL 
Z-80 uP PRODUCED BY ZILOG INCORPORATED. WHAT'S SO REVOLUTION- 
ARY ABOUT THE Z-80? A LOOK AT THE FOLLOWING COMPARISONS 
WILL SHOW YOU: 

As you can see, the Z-80 is a very 
powerful and fast uP - in fact its a NEXT 
generation microprocessor. And its 
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with a NEXT generation uP. The power 
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tremendous developments in the state of 
the art. More powerful, faster, and less 
memory consuming versions of your 
current 8080 software are just a part of 
the possibilities the Z-80 provides. (TDL's 
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available in September.) 

Each Z-80 CPU kit comes complete with: 

• Prime commercial quality boards, IC 
sockets etc. 

• easy to follow instructions 

• Zilog's Z-80 Manual 

• Schematics 

• An easy to understand and apply user's 
guide 

• TDL's Z-MONITOR on paper tape (soon 
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• And membership in the Z-80 user's 
group. 

Move up to the Z-80. Only $269. 

THE FASTEST RAM? The high speed 
capability of the Z-80 demands an extra- 
fast RAM to back it up, and TDL's new 
Z8K RAM board fills the bill. The Z8K is 
an 8K by 8 static RAM with the fastest 
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Its the only RAM in personal computing 
fast enough to let the Z-80 run at full 
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enough, it also happens to be one of the 
lowest powered RAMs around as well. 
Only 150 ma typical current load on the 
5V supply. That makes the Z8K run cool 
-and perfect for battery standby opera- 
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WHAT ABOUT QUALITY? All TDL 

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to keep your system state of the art at the 
lowest possible cost. Consider also the 
"Qual Division" whose ONLY purpose is 



Comparison of the Zilog Z-80, Intel 8080 


and Motorola 6800CPU chips 




Z80 




8080 


6800 


NUMBER OF: 










Instructions 


158* 




78 


72 


Internal Registers 


17 




7 


6 


Addressing Modes 


10 




7 


8 


Voltage Required 


+5 




+5,-5,+12 


+5 


Standard Clock Rate 


DC-3MHz 


0.5-2MHZ 


0.1-IMHz 


Clock Phases 


1 




2 


2 


Clock Voltage 


4.2 




8.4 


4.8 


DynamicRAM refresh and timing signals 










without slowing down CPU or 










requiring additional circuitry 


Yes 




No 


No 


Single instruction memory to memory and 










memory to I/O BLOCK TRANSFERS 


Yes 




No 


No 


Single instruction SET, RESET, or TEST 










of any bit in accumulator, any 










general purpose register, or any 










external memory location 


Yes 




No 


No 


Single instruction BLOCK SEARCH of 










any desired length of external 










memory for any 8-bit character 


Yes 




No 


No 


Non-Maskable Interrupt and TTL 










compatible inputs 


Yes 




No 


Yes 


Internal sync of inputs and direct 










strobe of outputs 


Yes 




No 


No 


* Includes all 78 machine code instructions of th 


e 8080A 


and is therefore 


capable 


of running any standard 8080A software 


without modification. 




ADDITIONAL FEATURES OF THE Z-80: 










• Up to 500% more throughput than the 8080A 








• Requires 25% to 50% less memory 


space 


than the 8080A nrii 


• Three modes of fast interrupt response 


plus a 


non-maskable 


interrupt 


• Outperforms any other microcomputer 


n 4-, 


8-, 16-bit applications 



to keep TDL's products the best in the 
industry. And our products use only the 
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SAVE MONEY NOW Order both a Z-80 
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HOW TO ORDER Just send check or 
money order, or use your BankAmericard 
or Mastercharge, and your orders will be 
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COD orders must be accompanied by a 
25% deposit. Your credit card order must 
include the serial # of the card, expiration 
date, and your order must be signed. New 
Jersey residents add 5% state sales tax. 
For more information, send for our free 
catalog. 

Dealer Inquiries Invited 



TDL 



(609) 392-7070 
39 



/TECHNICAL DESIGN LABS INC. 
342 COLUMBUS AVENUE 
TRENTON, NEW JERSEY 08629 



BYTE Reprint 



Chapter 2 



MACHINE LANGUAGE 
PROGRAMMING FOR THE "8008" 
and similar microcomputers 



Reprinted from MACHINE LANGUAGE 
PROGRAMMING FOR THE "8008" (and 
similar microcomputers). 



Author: Nat Wadsworth 
Copyright 1975 
Copyright 1976 - Revised 
Scelbi Computer Consulting Inc 
With the permission of the 
copyright owner. 



INITIAL STEPS FOR DEVELOPING PROGRAMS 



The first task that should be done prior 
to starting to write the individual instruc- 
tions for a computer program is to decide 
exactly what it is that the computer is to 
perform and to write the goal(s) down on 
paper! This statement might seem unneces- 
sary to some because it is such an obvious 
one. It is stated because the majority of 
people learning to develop programs will 
realize its significance when they discover, 
halfway through the writing of a large mach- 
ine language program, that they left out a 
vital step. Such an error can typically result 
in the programmer having to start back at 
the beginning and rewrite the entire pro- 
gram. The practice of writing down just 
what tasks a particular program is to perform 
and the steps in which they are to be done, 
will save a lot of work in the long run. The 
written description should be as complete 
and detailed as necessary to ensure that 
exactly each step of the program will be 
clear when actually writing the program in 
machine language. It is generally wise for 
the novice programmer to take pains to be 
quite detailed in the initial description. 

The act of actually writing down the 
proposed operation of the program desired 
serves several valuable purposes. First, it 
forces one to carefully review what is 
planned. In doing so, it often vividly 
reveals flaws in original mental ideas. 
Secondly, it serves as a guide and a check 
list as the machine language program is 
developed. Remember, it will often take 
a number of hours to write a fair sized 
program. These hours might be spread over 
several days or weeks. In this period of time 
the human mind can easily forget original 
intentions and plans if the human memory 
is not refreshed by written notes. A pro- 
gram that is not kept carefully organized 



as it is developed can become a real mess. 
This is especially so if one keeps forget- 
ting key concepts or has to constantly 
add in forgotten routines. The time wasted 
by such sloppy procedures can be avoided 
if proper work habits are developed from 
the beginning. 

Once one has written a description of 
the general task(s) to be performed, and 
has ascertained that there are no flaws to 
the overall concepts or ideas, it is a good 
idea to draw up a set of FLOW CHARTS 
for the proposed program. FLOW CHARTS 
are detailed written and symbolic descrip- 
tive diagrams of the flow of operations 
that are to occur as the program is executed. 
They also show the interrelationships be- 
tween different portions of a program. 

Over the years a variety of symbols and 
methods have been developed for creating 
flow charts. All of the varieties have the same 
basic purpose and most of the differences are 
the result of individuals pushing their own 
preferences. Most people can do admirably 
well using just a few basic symbols to denote 
fundamental types of operations in a com- 
puter program. The small group to be pre- 
sented here will enable most microcomputer 
programmers to develop flow charts rapidly, 
with little confusion, and without having to 
learn a host of special symbols. 

A CIRCLE may be used as a general 
purpose symbol to specify an entry or exit 
point in a routine or subroutine. Information 
may be printed inside the circle. This in- 
formation might denote where the routine 
is coming from or going to (such as the page 
number and location on a page for a program 
that requires several sheets of paper to be 
flow charted). It might contain transfer 



40 



information. Or, it could denote the starting 
and stopping points within a program. Some 
typical examples of the CIRCLE symbol 
are illustrated next. 



( START j 

| FM \ 
I TTY J 




Lines with arrows may be used to inter- 
connect the three types of symbols pre- 
sented. In this way, the. symbols may be 
connected to form readily understood FLOW 
CHARTS of operations that are to occur 
in a program and to show how various 
operations relate to each other. Flow charts 
are extremely valuable references when 
developing programs as well as when one 
wants to update or expand a program and 
needs to quickly review the operation of the 
program of specific interest. 

An example of a flow chart for a relatively 
simple program will be shown next. The pro- 
gram illustrated by the flow chart is to accept 
characters from an ASCII encoded electric 
typewriter and send out the equivalent 
character to a BAUDOT coded device. In 
this illustration it is assumed that the I/O 
interfaces to the machines are parallel inter- 
faces (versus the possibility of being bit- 
serial interfaces). Thus, complex timing 
operations do not have to be discussed in 
the example. A written description of the 
example program could be stated as follows. 

The computer is to monitor bit B7 of 
INPUT PORT 01, which is the control port 



for an interface to an ASCII encoded elec- 
tric typewriter. Whenever bit B7 on INPUT 
PORT 01 goes low (logic '0') it indicates a 
new character is waiting in parallel format 
from the typewriter at INPUT PORT 00. 
The computer is to immediately obtain the 
character that is waiting at INPUT PORT 00 
and as soon as it has obtained the data it is 
to send a logic '1' (high) signal to bit B0 of 
OUTPUT PORT 11 to signal the ASCII in- 
terface that the character has been accepted 
by the computer. (The receipt of this signal 
by the ASCII interface will then cause the 
ASCII interface to restore the control signal 
on bit B7 of INPUT PORT 01 to a high 
(logic '1') condition.) 

Whenever a character has been received 
from the ASCII typewriter on INPUT PORT 
00, the computer is to compare the charac- 
ter just received against an ASCII to 
BAUDOT look-up table which is stored in the 
computer's memory until it finds a match. It 
will then obtain the equivalent BAUDOT 
character from the conversion table. It will 
then send the BAUDOT code for the charac- 
ter in bit positions B5 through B0 of 
OUTPUT PORT 10. Bit B5 will serve to in- 
dicate to the BAUDOT interface whether 



A square or rectangel may be used to 
denote a general or specific operation. The 
type of operation may be described inside the 
box such as illustrated in the following 
examples. 



| CLEAR THE ACCUMULATOR! 



STORE THE 
INCOMING 
MESSAGE 



SET 

I/O 

FLAGS 



A diamond form may be used to symbolize 
a decision or branching point in a program. 
The determining factor(s) for the decision or 
branching operation may be indicated inside 
the symbol. The two side points of the 
diamond are used to illustrate the path 
taken when a decision has been made. The 
diamond symbol is illustrated next. 





GET ASCII 

CHARACTER 

FROM INPUT 

PORT 00 



SEND A LOGIC TON B0 

OF OUTPUT PORT 11 TO 

CLEAR THE ASCII 

INTERFACE 



GO TO LOOK-UP TABLE 
ROUTINE AND FIND 
THE EQUIVALENT BAUDOT 
CHARACTER 



SEND THE BAUDOT CODE 

TO OUTPUT PORT 10 IN 

BITS B5 THROUGH B0 




41 




the code in bits B4 through BO is to be pro- 
cessed by the BAUDOT device when it is in 
the LETTERS or FIGURES mode. It is 
assumed that the character rate (but not 
necessarily the baud rate) is the same for both 
machines so that the example may be simpli- 
fied by eliminating the requirement for 
character buffering or stacking in the memory 
of the computer. However, in practical appli- 
cations such capability might be required. 
The feature could be added to the program. 
However, for this case, as soon as the 
BAUDOT code has been transmitted (in 
parallel format) to the BAUDOT device, the 
computer will simply go back to waiting for 
the next character to come in from the ASCII 
machine. The written description of the pro- 
gram just presented is succinctly summarized 
in the flow chart shown on the previous page! 

The flow chart of the program shown on 
the previous page could be considered an 
outline of the program. Portions of that flow 
chart could be expanded into more detailed 
flow charts to present a detailed view of 
special operations. For instance, the rectangle 
labeled GO TO LOOK-UP TABLE ROUTINE 
AND FIND THE EQUIVALENT BAUDOT 
CHARACTER really refers to a portion of the 
program that consists of a number of opera- 
tions. Those operations could be described 
in a separate flow chart such as the one just 
presented . 

The reader can see that the expanded 
flow chart illustrates the operation of the 
table look-up routine portion of the program. 
With a little study one can discern that the 
look-up table consist of an area in memory 
that has an ASCII encoded character in one 
word, followed in the next word by the 
same character in BAUDOT code. This 
sequence continues for all the possible 
characters as illustrated below. The flow 
chart illustrates how the data in the look-up 
table is scanned by skipping over every other 
memory location (which contains the 
BAUDOT codes) until the proper ASCII 
character is located. When that is located, 
the routine simply extracts the proper 
BAUDOT code from the next memory 
locaction in the table. The flow chart makes 
the sequence easier to understand than a 
purely verbal explanation of the routine. 




INITIALIZE POINTERS TO 
START OF LOOK-UP TABLE 



COMPARE THE CONTENTS OF THE 

CURRENT LOCATION IN THE LOOK-UP 

TABLE AGAINST THE CHARACTER 

PRESENTLY IN THE ACCUMULATOR 



NO 




YES 



ADVANCE THE 
TABLE POINTER 
BY TWO WORDS. 



HAVE FOUND THE DESIRED 

CHARACTER. ADVANCE THE 

POINTER TO THE NEXT WORD 

IN THE TABLE AND FETCH 

THE BAUDOT EQUIVALENT. 



( EXIT J 





ADDRESS 




PAGE 


XX LOC 


z 


PAGE 


XX LOC 


Z+l 


PAGE 


XX LOC 


Z+2 


PAGE 


XX LOC 


Z+3 



PAGE: XX LOC: Z+2(N-1) 
PAGE: XX LOC: Z+2(N-1)+1 



MEMORY CONTENTS 

ASCII code for letter A 
BAUDOT code for letter A 
ASCII code for letter B 
BAUDOT code for letter B 



ASCII code for N'th letter 
BAUDOT code for N'th letter 



ILLUSTRATION OF LOOK-UP TABLE ORGANIZATION FOR THE EXAMPLE PROGRAM 



It is strongly recommended that beginning 
programmers develop the habit of first writing 
down the function(s) of the desired program 
they intend to create. Next, one should draw 
up flow charts as detailed as one feels is neces- 
sary to clearly show the operation of the pro- 
gram that is to be developed. A novice pro- 
grammer will be wise to prepare quite detailed 
flow charts. More experienced programmers 
may prefer to leave out details of operations 
that they thoroughly understand. Flow charts 
should serve as ready references when the pro- 
grammer goes on to actually develop the step- 
by-step machine language instruction sequen- 
ces for the computer. 

Flow charts are also an excellent method 



for communicating programming concepts 
to fellow computer technologists. 
Remember that general flow charts do not 
have to be machine specific!) Learning how 
to prepare and read flow charts is an 
important (yet easy) skill for all computer 
programmers to acquire. It can also be fun 
and a highly creative process. Using the 
technique, one may review the overall 
operation of a program under development 
and gain new insights into where to 
interconnect routines, where common loops 
exist (which can save valuable memory room 
if they are subroutined), and find other ways 
in which to enhance a program's 
capabilities. 



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42 




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Telephone: 203/874-1573 



Milford, CT 06460 



True Confessions: 
How I Relate to KIM 



I recently purchased a KIM-1 micro- 
computer card from MOS Technology (See 
"KIM-O-Sabee?" in the April BYTE, page 14 
and "A Date With KIM" in the May issue, 
page 8). In my opinion, KIM-1 offers one of 
the best bargains to a computer experi- 
menter for the price ($245 for the card + 
$4.50 for shipping and handling). However, 
the hobbyist may be faced with a few 
problems, as I was. The intent of this article 
is to solve some of these problems. 



Yogesh M Gupta 
118 E Main St 
New Concord OH 



43762 



ICI 

7404 



560 n 



560fl 



■►MtffrMS* 



.02fLF 



AH 



2.0MHz CRYSTAL 







+ 5V 


ICI 


740 4 


14 


IC2 


7474 


14 


IC3 


7400 


14 


IC4 


74103 


4 



SPEED SELECT 



R W 
(FROM 6502) 




Clock Stretch and 
Random Access Memories 

The cheapest random access memory in 
experimenters' markets today is the standard 
2102 static memory which averages approxi- 
mately 0.1 5</ per bit. During a write cycle, 
the inexpensive slow versions of this device 
require the data to be stable for 800 ns 
before the trailing edge and data hold time 
of 100 ns after the trailing edge of the write 
pulse. Even if the MOS Technology 6502 
processor is slowed down to 250 kHz to 
obtain the data stability, there is still not 
enough data hold time for the slow chips. 

I solved this problem by implementing 
the circuit shown in figure 1. This circuit 
allows the 6502 processor to use a mixture 
of fast and slow 21 02 memory devices in the 
same system. The processor cycle is main- 



I — ^o-O 

—* y (TO SL 



Figure 1: A circuit which 
creates an alternative slow 
clock cycle for the 6502 
processor on the KIM-1 
board under control of a 
"SPEED SELECT" line 
generated by slow mem- 
ories. SPEED SELECT =0 
for fast cycles, SPEED 
SELECT = I for slow 
cycles. This circuit re- 
quires a 2.0 MHz crystal. 



SLOW 
2102's) 



44 



U— 12 -J 

Uti-rt I 

I I L 



*0 (IN) 



■A 



» I (6502) 



ADDRESS BUS 
(6502) 



SPEED SELECT 






"L 



FAST 
CYCLE 



zm 



SLOW 
CYCLE 



tl = 500nS 

t2 = lOOOnS 

13 = 75 nS - MAX. 

14 = 300nS-MAX. 

t5 = TIME FOR ADDRESS DECODER 



Figure 2: Method 1 
SPEED SELECT Dis- 
cipline. In this method, 
fast cycles are' the rule, 
slow cycles are the excep- 
tion. Refer to figure I for 
points B and C. Invalid 
data on the address bus is 
indicated by the cross- 
hatched areas. 



tained at 1.0 /is for the fast memory access, 
while for the slower 2102s, the cycle is 
automatically stretched to 2.0 jus. 

Sometimes integrated circuits behave in 
ways that are not predicted by, or are 
overlooked by, their manufacturers. This 
modification of KIM-1 to enable the clock 
stretching function is accomplished by re- 
moving the usual KIM-1 6502 clock genera- 
tion circuitry, and simply driving the 0fj pin 
of the 6502 directly from a TTL clock 
source which is external to the chip. This 
mode of operation is not documented in the 
6502 Hardware Manual of MOS Technology, 
but it worked quite satisfactorily in my 
system . The intention of the designers of the 
6502 was that the clock generation logic on 
the chip would be used with external com- 
ponents setting the frequency of the 
oscillator. 

The SPEED SELECT signal to stretch the 



POINT B 
POINTC 

*0(IN) 
6502 PIN37 

*l(6502) 



ADDRESS BUS 
(6502) 



- (2 

♦ tl-H 



SPEED SELECT 



am, m 



SLOW CYCLE 



FAST 
CYCLE 



tl - 500nS 

t2 « lOOOnS 

(3 ■ 75 nS MAX 

t 4 = 300nS MAX 

15 ■ TIME ALLOWED FOR ADDRESS DECODER 



Figure 3: Method 2 
SPEED SELECT Disci- 
pline. In this method, slow 
cycles are the rule, fast 
cycles are the exception. 
Refer to figure 1 for 
points B and C of the 
timing diagram. Invalid 
data on the address bus is 
indicated by the cross- 
hatched areas. 





h- i2 -H 

r*ti-H 


r 






r 

L 
L 


ii = 

12 = 

13 ■ 
t4 • 

15 - 

16 ■ 


250 nS 


POINT A 


i— \_r 


i I 


500nS 








90nS MAX 
200 nS MAX 


POINT B 


i i 


— L 


I 




950 nS 


*0 (IN) 






350 nS 


i i 










#j h<3 




4>2(6502) 


"i r~ 

•114 


K 




1 




DATA BUS (6502) j 


JZ 




R 








h — 




«-16 


■H 










RW FOR 
SLOW 2102 S 









Figure 4: Write Cycle for Slow 2102 Mem- 
ories. The timing requirement is that valid 
data be present on the bus when the RW 
signal to the memory changes from (write 
state) to I (read state). The crosshatched 
areas indicate when data is invalid on the 
data bus. 



45 



ICI 

560 a 74 ° 4 



.02/iF 



560ft 



1.0 M 



I.0MH2 

| CRYSTAL 



POWER CONNECTIONS 




+5V GND 


ICI 7404 


14 7 


IC2 7474 


14 7 


IC3 7400 


14 7 


IC4 74123 


16 8 



»2 r- v^ 

FROM KIM-I I ^ 



+ 5 
t R 

US 



+ 5 



IC2 
CLK 
7474 



I 
IOK 



RW FROM i — ^ 
KIM-I LJ>~ 



+ 5 



CL 

B Q 

IC4 
A 
74123 

CX RX 



400pF 



T 



15 



V 



POINT 
C 



ICI 



9 !> 8 - 



IC3o^3 
2|7400 



IC3b V 



517400 



-<2]SPEED SELECT 



-O»o 

TO 6502 
PIN 37 



<3 



RW TO 
SLOW 2102 S 



Figure 5: Alternate Slow 
Clock Generation Circuit. 
In this circuit, the original 
KIM-I crystal can be used, 
since a digitally controlled 
timing cycle is replaced by 
the 74123 oneshot. 



cycle is generated by address bus decoding 
logic using one of the following two 
methods. 

Method 1: Normally the SPEED 
SELECT signal is kept low so the proces- 
sor cycle is 1.0 /is. However, this signal 
goes high when the processor addresses 
the slow memory region causing the cycle 
to stretch to 2.0 /is. See figure 2 for the 
timing relationships. 

Method 2: Normally the SPEED 
SELECT signal is kept high so that the 
processor cycle time is 2.0 /is to access 
slow memory. However, this signal goes 
low when the processor addresses the fast 
memory devices causing the cycle time to 



42(6502) 



DATA BUS 



2/xS 



«-500nS-»| 



•J K 



200nS 



(6502) ^ 



WWWVW^i 



M 



RW FOR " 
2102 



l.0 M S »\ j 

-»)300nsU- 



Figure 6: Write Cycle for Slow 2102 Mem- 
ories using the circuit of figure 5. The 
output pulse width of RW is adjusted to 
1.2 lis nominally. (Check the results on your 
scope even if you use other than precision 
parts of the values shown for Ri and CI in 
figure 5.) 



be only 1 .0 /us. See figure 3 for the timing 

relationships. 

The circuit shown in figure 1 will allow a 
data stability of 950 ns before the trailing 
edge and data hold time of 350 ns after the 
trailing edge of the Write Pulse for the slow 
2102s. See figure 4 for the timing relation- 
ships. 

However, the KIM-1 board comes with a 
1.0 MHz crystal. Figure 5 shows an alter- 
native circuit using a 1.0 MHz crystal. The 
timing relationships to control SPEED 
SELECT signal are the same as shown in 
figures 2 and 3. The RW signal for the slow 
memory is generated in this case by using a 
74123 oneshot. The value of the RC 
constant for the 741 23 is chosen to provide 
a nominal output pulse width of 1 .2 /is. This 
allows a data stability of 1 .0 /is before the 
trailing edge and data hold time of 300 ns 
after the trailing edge of the write pulse for 
the slow memories. Figure 6 shows the 
resultant timing relationships. It should be 
noted that the output pulse width of the 
74123 can only tolerate a ±16.66% 
variation, and still permit successful opera- 
tion of the 2102 memory devices. This 
tolerance may require selection of precision 
parts for the external resistor and capacitor 
of the oneshot. 

Bus Expansion 

The 6502 bus is only capable of driving 
one standard TTL load. If more drive 
capability is needed, the tristate drivers such 
as the 8T97 or DM8833 parts may be used. 



46 



I— 



6502 

DATA LI 



" mC Lp. 



R W 
(6502) d>- 



~<a 



i — <Hf 



BUS EXTENSION INTEGRATED 
CIRCUIT. TYPICAL PARTS: 

DM8833 

8 T97 



-<^) HIGH DRIVE CAPABILITY TRI- 
STATE 



Figure 7: Use of a Bus Extension Integrated Circuit. In order to tie in extra 
memory or peripherals, a bus extension is required. The typical logic diagram 
of a simple attempt which will not always work is shown here. (Conflicts can 
arise.) 



However, you must be very careful when 
using an extended data bus. If you enable 
the drivers by RW signal as shown in figure 
7, then during read mode, the drivers for the 
existing KIM-1 memory (eg: 74125s) can be 
turned on simultaneously. The low level 
output current of 741 25s is only 1 6 mA and 
is not sufficient to pull down a turned on 
8T97 type driver to logic level. Therefore, 
during read mode the bus extension tristate 
drivers should be turned off when the 
existing on board KIM-1 memory (RAM, 
6530-002 and 6530-003) is being accessed as 
shown in figure 8. In actual implementation 
the DECODE ENABLE signal may be the 
same as the one needed on the application 
connector of the KIM board (when more 
than 8 K memory is needed). 

Interrupt Prioritizing Logic 

The KIM-1 Hardware Manual (Section 
2.3.3) describes a few approaches to im- 
plement interrupt priority logic; but I found 
them either inefficient (software time) or 
expensive (use of ROM). The circuit shown 
in figure 9 provides a cost effective com- 
promise. The interrupts from the peripheral 
devices are latched in by the 02 signal. This 



inhibits the priority encoder from generating 
a false vector (if the interrupts from the 
peripherals are changing while the 6502 is 
fetching the vector). In response to IRQ, the 
6502 fetches the vector from hexadecimal 
locations FFFE and FFFF. During these 
fetch cycles, the 6530-002 is disabled by 
letting the decode enable signal go high on 
the application connector. Therefore, the 
vector generated by this circuit is fetched by 
the 6502 instead, and the program goes to 
one of the locations from 0200 to 021 C. 
This segment of memory serves as a vector 
table with pointers to the individual inter- 
rupt service routines as follows: 

0200 J MP VEC0 

0204 J MP VEC1 

0208 JMP VEC2 

020C JMP VEC3 

0210 JMP VEC4 

0214 JMP VEC5 

0218 JMP VEC6 

021C JMP VEC7 

The actual service routines will reside in 
locations VEC0 through VEC7 for the 
respective interrupts. It should be noted that 
each vector in the table requires 4 locations. 
(Only 3 locations are needed for a jump but 



6502 i— ^_ 

DATA LINE I — ->~ 



ihl 



i> 



I __ 



RW(650Z>O-i ^1 

DECODE i— >J 7° 

ENABLE I >— t y 



• BUS EXTENSION INTEGRATED 
CIRCUIT. TYPICAL PARTS: 
DM8833 
8T97 



-< | HIGH ORIVE CAPABILITY TRI- 
STATE 



Figure 8: Adding a gate to 
the bus extension control 
resolves a potential con- 
flict through the use of a 
decode enable signal which 
is high if external memory 
is referenced, low if mem - 
ory on the KIM-1 board is 
referenced. 



47 



INTERRUPTS 

FROM 

PERIPHERALS 



BUFFERED/ 
ADDRESS \ 
LINES 




SYSTEM DATA 
)BUS 
EXTENSION 



HIGH DRIVE CAPABILITY 
BUS INTERFACE 
EG:DM8833 
8T97 



IC9 
7400 



ADDRESS 
FFFE/FFFF 
ARBITRARY 
ADDRESS 



^j 9° y~~<3 







DISABLE 




POWER PINS 






+5V GND 




ICI 


74175 16 8 




IC2 


74175 16 8 




IC3 


74158 16 B 




IC4 


7408 14 7 




IC5 


7404 14 7 




IC6 


7430 14 7 




IC7 


7430 14 7 




IC8 


7432 14 7 




IC9 


7400 14 7 





DECODE ENABLE 
TO KIM 

APPLICATIONS 
CONNECTOR 



BUFFERS-PER CHOICE 



Figure 9: By disabling normal address decode through the DECODE ENABLE pin for the 
KIM-1 applications connector, an alternate source of the interrupt vector at locations FFFF 
and FFFE can be created which accomplishes interrupt prioritizing functions. 



the extra location is a requirement of a 
simple hardware design.) J MP instruction 
takes only three locations, so your software 
might use the fourth location to save the 
accumulator, eg: 

0200 PHA 

0201 J MP 

0202 VECO (LOW) 

0203 VECO (HIGH) 

This architecture will re-map the 1 K 
resident RAM on the KIM board as follows: 
0000 through OOFF Page 
0100 through 01 FF Stack 
0200 through 021 F Vector Table 
0220 through 03FF Applications 
The disable signal in figure 9 will deselect 
existing KIM-1 memory when low. This is 
implemented for memory expansion as 
described earlier. However, if memory ex- 
pansion is not desired the signal may be 
fixed to a logic 1 level. 



Halt? 

Another problem -one faces is how to 
debug the software when the processor does 
not have a HLT instruction. You can single 
step the program instructions on KIM-1, but 
this feature does not help the programs 
which involve multiple levels of loops or 
critical peripheral timing controls. The 
obvious solution is to use the BRK (software 
interrupt) instruction. However, this would 
require software overhead in every interrupt 
service routine to determine whether it was a 
hardware or a software interrupt. On the 
KIM-1 system, I found the sequence JSR05 
1C (Jump to subroutine at location 1C05) 
more useful for this purpose instead. The 
execution of JSR causes the program to 
jump to an input monitor loop and display 
of the address (PC + 2) on the KIM board. 
PC is the location where the JSR was 
executed." 



48 




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Intellec is a trademark of Intel Corp. 



What's 

New? 



New Products Policy 

Insertions in this section of BYTE are 
chosen at our discretion from unsolicited 
"press release" materials sent by vendors. 
New companies inexperienced in the game 
of publicity seeking are advised that a press 
release on a hardware product should con- 
tain a descriptive text plus glossy black and 
white photograph (or photographs) of the 
item. Software products should include 
ample descriptive text to convey an idea of 
what is being marketed; if there are any 
characteristic graphic materials associated 
with the software product, pictures or 
camera ready copy should also be supplied. 

Appearance of descriptive information on 
a product in these columns does not con- 
stitute an endorsement of that product." 



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The basic price of the unit is $295, which 
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and delivery is quoted as being from zero to 
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Parallel Interfaced Audio 
Cassette Driver 

Custom Design Services, 4021 Windsor, 
Garland TX 75042, sent along this picture of 
the CI-810 tape interface board. The circuit 





|^^*'-^H 




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of this design, by Harold Mauch, appeared in 
BYTE's March [page 43] and April [page 
10] issues. The design uses the modified 
Manchester encoding scheme of the audio 
interface standards conference organized by 
BYTE in November 1975, and runs at 27.27 
bytes per second (300 Baud). 

The modulator and demodulator can be 
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pin double sided edge connector, has room 
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Power requirements are 5 V at 100 mA, 
—12 V at 15 mA, 5% regulation on both 
supplies. 

The price for this single channel interface 
is $59.95, and the unit is supplied with 
complete documentation of its interface 
requirements and operation. ■ 



Make Hard Copies With This Printer 

The mp-40 is a low cost impact printer 
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The number of moving parts has been 
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of 40 characters. A standard width (12 
characters per inch) character or an ex- 



50 




tended width (6 characters per inch) charac- 
ter can be printed under software control. It 
prints a 64 character ASCII set with 6 lines 
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The completely assembled and tested mp-40 
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The National Multiplex Corporation, 3474 
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details of the software in this monitor, 
contact National Multiplex, which sells the 
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If you want a microcomputer 
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• Complete with card 
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• Optional ac- 
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Telephone (217) 367-7373 



51 



One day in 1975, Jack had finally had it with ma- 
chine language. 



Jack and the Machine Talk 

(or, the Making of an Assembler) 



Robert D Grappel 
148 Wood St 
Lexington MA 02173 

Jack Hemenway 
151 Tremont St 
Boston MA 021 11 



One day in 1975, Jack Hemenway had 
finally had it with machine language. "I'm 
tired of address calculations in hexadecimal! 
I'm tired of looking up every opcode! My 
Motorola manuals are falling apart! I'm tired 
of midnight debugging from memory 
dumps! My eyes ache from reading page 
after page of hexadecimal! I need a good 
bookkeeper to help me write programs, 
someone who knows Motorola opcodes by 
heart, can compute in hexadecimal, is in- 
fallible! A bookkeeper I can really talk to!" 

Jack thought about this problem for 
some time. Finally, he decided to make his 
new microcomputer become his bookkeeper. 
The processor was aghast. 

"I've never written a program myself! I'd 
never know where to begin!" 

Jack calmed his agitated MPU and assured 
it that he'd never leave it completely alone, 
and besides, he was going to teach it to 
program for him. "You'll see how easy it is, 
really." 

"First of all, I want you to memorize this 
list of Motorola opcodes and their 
mnemonics. Then, you can tell me the 



hexadecimal opcode for any instruction, and 
I won't have to remember which is which. 

Computer cycled for a while, its lights 
flashing. Then, it halted. 

"OK," said Jack to his 6800, "Now, what 
is an RTS instruction?" 

The computer began leafing through its 
copy of Motorola opcodes and after several 
milliseconds of thought responded, "That's a 
return from subroutine. . . hexadecimal 39." 

"Fine," said Jack, "How about CLR?" 

The computer hesitated only a moment 
before responding, "That's a clear instruc- 
tion . . . hex 7F." 

"That's fine, computer, but you take too 
long to look up mnemonics. You do a lot of 
searches before you come to the item I ask 
for; and if I slip up and ask for an invalid 
mnemonic, you've got to search through all 
the valid ones in your dictionary before you 
know about my error. I'm going to show 
you a better way." 

Jack then taught his computer the binary 
search method. "You see, the mnemonics 
are ordered in alphabetic order." 

"What's an alphabet?" 



52 




"Oh, I forgot how finicky you are about 
new terms," said Jack. "Let's just say that 
they are ordered in ascending sequence." 

"That's better," sighed computer. "Num- 
bers I understand!" 

Jack continued, "You presently start 
searching at the first entry in your table. I 
suggest that you start with the middle entry. 
Since I am going to provide you with a 
program that can test the ordering of entries, 
you will then be able to tell whether the 
mnemonic you want lies in the first or 
second half of the table. As you see, now 
you need search only half the table." 

"Great," interrupted computer, imme- 
diately trying out its new program. 

"Wait!," said Jack, "I'm not finished yet, 
and neither are you!" 

"All right, Jack," replied the computer, 
sheepishly executing wait states. 

Jack continued, "You can use my new 
program over and over again. Each time you 
use it, you'll reduce the length of table you 
need to search by a factor of two. Finally, 
you'll either have the desired mnemonic 
or you'll know that it isn't in the table. For 
a table like the one I gave you, this process 
will take about one sixth the number of 
searches you have been requiring. 

"Computer . . . what's an STA instruc- 
tion?" 



"You know I can't tolerate ambiguity! How do I 
figure out which definition to use ... ?" said the com- 
puter petulantly. "I 'm going to provide a grammar for 
you too ..." replied Jack unambiguously. 



"That's a store accumulator instruction," 
replied the computer almost instantly, "but 
there is more than one possible opcode for 
it. Do you want accumulator A or B? What 
kind of addressing do you want?" 

"I see that we have much more to learn. 
Right now, just remember that it is a store 
accumulator instruction. I'm going to have 
to specify a language with which to answer 
your questions. I'll teach it to you soon." 
Jack reached over and turned off the power 
supply. The fan slowly whirred to a stop. 



"Wakeup, you lazy machine," called Jack 
from his fancy CRT terminal. 

"Who, what, where?????", mumbled the 
computer as its power rose to its accustomed 
level. 

"It's time for your next lesson in pro- 
gramming." Jack began to type in a list of 
characters. He typed in the alphabet, the 
digits, add, subtract, multiply and divide 
symbols, punctuation, and some special 



Jack walked down the hall 
and turned off the room 
lights. Only computer's 
red panel lights could be 
seen, flickering 
seductively. 



53 



"You mean I have to take up my valuable memory 
with your comments?" interrupted computer in- 
dignantly. "Now don't get warm. All you need do 
with my comments is print them ..." replied 
Jack soothingly. 



symbols. With each character he added a 
defining hexadecimal byte. "Computer," 
Jack said as he turned from the keyboard, 
"you now know all the characters I'll ever 
use in talking with you. The definition byte 
will tell you what uses can be made of the 
character. If bit 7 of the character definition 
byte is set, you'll know that the character is 
a letter. If bit 6 is set, you'll know that the 
character is a digit. Bit 5 defines an arith- 
metic operator. Bit 4 defines a location 
separator. Bit 3 defines a mnemonic separa- 
tor. Bit 2 indicates an operand separator. Bit 
1 defines a hexadecimal character. And, not 
least, bit indicates a special symbol 
. . . namely A, B, or X. These will be the 
names I'll use to tell you about your 
registers and accumulators in my programs. 
You already know where these are." 

"Anything you say, Jack, but a lot of 
that last stuff was gibberish to me. Besides, I 
look at those character definition bytes of 
yours and it looks like some characters are 
more than one thing. You know I can't 
tolerate ambiguity! How do I figure out 
which definition to use? You haven't helped 
me much." 

"I'm going to provide a grammar for you 
too," answered Jack. "Anyway, you should 
be able to figure out a lot of the ambiguities 
yourself. . . especially if you're as smart as 
you tell me you are. Just remember that 
blanks separate every word I will say." 

"Sometimes your words are pretty blank, 
too!" 

"Very funny," said Jack, a bit peeved at 
his joking computerized bookkeeper. "But if 
I say '2,' you know that's the digit 'two,' 
right? And if I say '22,' it isn't hard to figure 
that I mean the number '22.' " 

"That's '16,' Jack. Remember, I work 
best in hexadecimal." 

"Ah yes, I remember," said Jack as he 
began to enter subroutines to convert strings 
of digits and the letters A through F to 
hexadecimal numbers. "Now, you can con- 
vert my numbers into your favorite form. 
I've taken the liberty of defining the dollar 
sign character as the signal for you to note 
that I've already converted to hexadecimal 
for you. Sometimes I like to work in 
hexadecimal myself . . . although I wish that 
I had 16 fingers to work with." 



"You could use your toes," suggested 
computer as it tried out its new software. 
"Let me see ... 128 is the digit '1 ' and the 
digit '2' and the digit '8.' It doesn't start 
with a dollar sign, so 1 have to convert to 
hex. That's 80 hex, right, Jack?" 

"Very good, you overgrown calculator!" 

"I don't mind the comparison. That 
reminds me, when are you going to give me 
programs to add and subtract. Multiple byte 
routines would be nice. My instruction set is 
a bit limited, you know." 

"Computer, brace yourself!" Jack sat 
back at the terminal, and he entered routines 
that did 16 bit addition, subtraction, multi- 
plication, and division. 

"Gee, Jack, you really outdid yourself. 
Are you sure I'll need all this stuff?" asked 
computer, while checking that 1225/5 really 
was 245. "Jack," said computer after be- 
coming satisfied with Jack's latest programs, 
"I could use some programs to convert my 
hex back to your decimal stuff. It'll help us 
communicate." 

"Sometimes I think we communicate too 
much already; but you're right, it would be 
nice if we did all our talking in one language. 
I'll have those programs for you tomorrow. 
Then, I'll start to teach you grammar." 

"Lovely, Jack, but could you leave my 
power on tonight? I'd like to exercise my 
new software some more. Don't want any 
bugs, you know." 

Jack walked down the hall and turned off 
the room lights. Only computer's red panel 
lights could be seen, flickering slowly. 



"Have a nice night of computing?" asked 
Jack as he ambled into the computer room 
next morning. "It's about time for your first 
lesson in my new language. We'll call it 
'assembler,' because it will help you 
assemble programs for me." 

"But Jack, I can barely understand you 
now! How do you expect another language 
to help either of us?" 

"Computer, I recognize how you hate 
ambiguity. My new language will force me to 
always be precise with you. Whenever I fail 
to cover all possibilities, you'll be able to 
point out my error. How about that?" 

"If you really think you're up to it, I'm 
all ears! My Teletype interface is itching for 
the touch of your fingers on my keyboard!" 

"First of all, computer, we'll state that 
each line of assembler is going to define one 
machine instruction. Even though I may 
write a many character line in assembler 
language, you'll be* able to find a single 
instruction that does what I want." 



54 



"Sounds good so far," said computer. "I 
always was more efficient in storing stuff 
than you are." 

"That's why I'm making you my book- 
keeper. Now — you'll read my stuff from 
left to right. Each line can have up to five 
parts. I'll guarantee that there will be at least 
one blank between each part of a line, and 
there will be no blanks between elements of 
the same part. You probably remember the 
'My Dear Aunt Sally' article in February 
BYTE; this is a simplification of its tokening 
process." 

"Fine. Then I can always skip blanks, 
right?" 

"Not quite, computer. The first character 
in each line is special. If it's an asterisk — 
remember your special symbols in the 
character table I gave you? — then the line is 
a comment of mine, and ..." 

"You mean I have to take up my valuable 
memory with your comments?" interrupted 
computer indignantly. 

"Now don't get warm. All you need do 
with my comments is print them. You don't 
have to remember them. That is, if your 
Teletype isn't too tired." 

"Boy, that's a load off my mind. I've got 
better things to remember." 

"You're certainly right there, computer 
of mine! But, as I was saying, if the first 
character of a line is an asterisk, then print it 
and be done with the line. If the first 
character is not a blank or asterisk, then I 
am labelling the line for some purpose. 
Labels are one of the parts of assembler 
statements that I want you to remember, 
since I'll likely want to refer to labels later. 
A label can be any combination of up to six 
characters, but all you need do is scan from 
left to right until you find a blank. If you 
can't find one, then you'll remind me with 
one of your wise guy error comments. I'll 
give you a program to scan lines just as soon 
as I finish describing the language." 

"Let me see, Jack. I've got to store away 
these labels of yours, and I should remember 
where I put them. They're really just ad- 
dresses, right?" 

"First prize, you animated TV set! I 
always knew you could handle this task once 
I converted everything into numbers for 
you." 

"Just as long as they're hexadecimal 
numbers, Jack. I need 16 bit addresses." 

"Two byte addresses you shall have," said 
Jack as he rose from his seat 'by the 
keyboard. "And you can probably guess 
what the second part of each assembler line 
is, since I've already told you that each line 
is equivalent to a single machine 
instruction." 



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"Look, Jack, don't insult my intelligence! I never 
forget, so long as you keep paying the power bill! " 



"I'll bet that you're going to tell me it's 
one of those mnemonics you made me 
memorize when we talked about opcodes." 

"Gee, your intuition is better than I 
expected from a microprocessor. The second 
item in each line will be a mnemonic. You 
already know how to handle them, remem- 
ber Binary search algorithm ..." 

"Look, Jack, don't insult my intelligence! 
I never forget, so long as you keep paying 
the power bill!" 

"No offense meant, old buddy. Now, you 
do remember the ambiguities we found in 
using the mnemonics. So, the third part of 
each assembler line will be called the 
operand field. There may be several 
operands or perhaps none, depending on the 
particular instruction format you're working 
on. The operands will tell you which accu- 
mulator to use, what kind of addressing I 
want to use, where the data to use is, and so 
on. I'll write subroutines to describe the 
form of each instruction in your repertoire so 
that you can figure out my operands. Ac- 
tually, there will be only a few of these 
routines, since many instructions share 
equivalent formats. I'll use blanks and 
commas to separate things. You can use 
your label scanner program to pick things 
apart." 

"Now those mnemonics make some 
sense, Jack. Thanks for all the new code. I 
see that you expect me to tell you about 
your 'dumb dumbs' as usual." 

"Just because you're too simple to make 
mistakes is no reason to get uppity! You 
should be able to figure out what instruction 
I want you to execute from the mnemonic 
and operands. There's another thing I want 
you to do for me. If I put a number sign in 
front of something, I want you to use that 
exact value in your instruction, not some 
address calculation or other of your weird- 
ities. We'll call it 'immediate operand,' 
because I'll expect you to process it imme- 
diately, with no computation." 

"I'm always eager to save myself com- 
putation, Jack. Let me see if I've got this 
right. I look at the mnemonic, find it in my 
mnemonic table by binary search, jump to 
the processing routine for that mnemonic 
type, break up the operands with the pro- 
grams you've so nicely supplied, and figure 
out which form of the instruction to use. 
This gives me an opcode to satisfy you. If I 



see a number sign in an operand, then I use 
that exact value, no matter how absurd it 
may appear at the time. Right?" 

"Right! One last thing though. You know 
how much I like to document things. My 
memory isn't as good as yours ... I some- 
times forget why I did a certain thing when I 
look it up later. I've made the last part of an 
assembler line a comment field. Just type it 
out just as you found it and we'll get along 
fine." 

"I'll do fine anyway, Jack. Just leave 
Teletype on. He could use the exercise." 



Computer cast a bleary red eye toward 
Jack as he entered the room. "This language 
stuff is hard. I've been studying all night, 
and I'm still not sure I've got it right yet." 

"OK. We'll review for a while. Suppose I 
tell you: 

LINE1 LDA A #11 THIS IS AN 
♦EXAMPLE OF AN ASSEMBLER LINE 

"If I understand this right, Jack, you have 
a load accumulator instruction there. You 
want me to put the value '1 1 ' decimal (or 'B' 
in my hexadecimal) into accumulator A. 
You also want me to remember the address 
of this instruction with the label name 
LINE1 . It will take two bytes of memory to 
store the instruction; one for the store 
instruction into accumulator A with imme- 
diate addressing, and a second for the value 
of the operand." 

"Very good, computer. Now try this 
one." 

LINE2 CLRB ANOTHER EXAMPLE 

"Your labels aren't particularly inspired, 
Jack. That's a clear accumulator B instruc- 
tion. One byte, with a new label. So far, 
your assembler programs don't do much for 
all my time in learning your language." 

"I leave you alone enough each night, 
now you do what I want. This is my test, 
not yours." 

INCB 

"OK, so I increment accumulator B. Big 
deal!" 

ERROR CRL 

*THIS IS NOT A VALID INSTRUCTION 



56 



"You aren't kidding there, Jack. That's an 
invalid mnemonic, or maybe you meant to 
have some operands? Did you really mean 
'CLR' instead? I could try to correct your 
mistake." 

"That won't be necessary; just flagging the 
error you find first is quite enough. I do the 
thinking in this association, remember that!" 

BGT LINE 2 

"Let me see about this, Jack. It's a 
branch on the condition that the last calcula- 
tion was greater than zero. Branches always 
use relative addressing, so I've got to figure 
out how many bytes I have to branch. I 
remember your label 'LINE2' in my mem- 
ory; it was the instruction to clear my B 
accumulator. Now what?" 

"I'll help you. The instruction at LINE2 
was how long?" 

"One byte." 

"What came next?" 

"An increment accumulator instruc- 
tion . . . another byte." 

"And next?" 

"A bad instruction that I couldn't under- 
stand, so I didn't generate any code for it. Is 
that all right with you?" 

"Fine. If I make a mistake, you just tell 
me about it and go on. It's my responsibility 
to use good assembly grammar. Now, the 



next instruction is the conditional branch 
you're working on now, right? How long is a 
branch?" 

"Two bytes. I still don't see what you're 
getting at, Jack." 

"Well, if you back up two bytes you're at 
the end of the increment code. Another byte 
back is the beginning of the increment. An- 
other byte back is the beginning of the clear. 
This is the point I labelled LINE2." 

"I get it, Jack! I just count up the 
number of instruction bytes I have gen- 
erated. You're simply asking me to do some 
simple counting for you, you lazy person. I 
want to branch backwards four bytes, which 
gives me a relative branch of minus four, or 
FC in hex. That's easy . . . even a human 
could do it. But, Jack, what do I do if you 
ask me to branch farther than 128 bytes? I 
can't count higher than that in a signed 
byte." 

"Just flag it as an error and go on." 
"Then it looks like I've got it figured! 
Test again, my brainy boss." 

LINE3 JMP LINE4 

*LET'S SEE WHAT IT DOES WITH THIS 

"Label is LINE3, it's a jump instruction, 
and you want me to transfer to an address 
symbolized by LINE4." The computer sat 



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57 



"I'm going to ask you to 
read my programs twice 
before you run them." 
said Jack. "But Jack, your 
programs usually aren't 
worth reading once!" re- 
plied computer testily. 



for a time, its lights flickering wildly. 
"TILT!!!! I can't do that, Jack! Your label 
isn't in my memory, and I never forget. I'm 
just going to have to skip this instruction." 

"Oops! Sorry, old buddy, but I'm going 
to have to ask you to handle stuff like that. I 
will want to be able to branch and jump 
around a program in any direction. I guess 
I'll have to make more use of your memory 
and patience. I'm going to ask you to read 
my programs twice before you run them." 

"Jack, your programs usually aren't 
worth reading once! Besides, how can that 
help? If I can't figure it out once, then I 
can't figure it out twice! We computers are 
like that, you know . . . consistent!" 

"Ah, but computer, you miss my point. 
You'll be doing different things in your two 
passes through the program. Your problem is 
that you may not see a label until after I 
want to use it as an address. So ... in pass 
one, you'll just look for labels. You'll locate 
every label in the program and compute its 
proper address in pass one. You'll need to 
decode each instruction in pass one to 
decide how many bytes it will take, but 
you'll generate no code until pass two. You 
can also call out most of the errors as you 
read pass one; then, I won't waste your time 
with pass two until I've corrected all the pass 
one errors. By the time you begin pass two, 
there should be no ambiguities left to 
trouble you. You can just go through and 
generate code without problems. " 

"I've still got a big problem, Jack. My 
memory is big, but you like to write all those 
comments and mnemonics and stuff in your 
programs. If I've got to remember it all, then 
I've got to have help. Lots of help! You 
aren't particularly efficient in this new as- 
sembler language." 

"Computer, remember that article I 
wrote for BYTE a while back? The one 
about using a cassette tape recorder to store 
data and other digital stuff? How about 
using a recorder to ease your memory 
burden?" 

"You're a real friend, Jack. I can keep all 
but one line of your stuff on tape. You'll 
give me programming to read from tape. 
Then I can read each line as I come to it, 
process it, and go ahead. I'll still need space 
for a table of labels, and tape buffers, but 
that won't be nearly as much trouble. I am a 
pretty good sized machine, after all." 

"I soldered every one of your connec- 
tions." There was a certain weariness in 
Jack's voice. "I'll give you all the programs 
you can use, and then some! You'll be 
running two tape recorders, you lucky ma- 
chine! You'll read in my stuff from cassette 
drive one in two passes. I'll do the rewinding 



for you; you just tell me when you want the 
tape rewound. In pass two, you'll put your 
generated code out to cassette drive two. 
Just be careful not to write over my tapes of 
Irish folk songs." 

"That I'll do, Jack, just as long as you 
keep your bagpipe music tapes off my input. 
Though they'd probably make interesting 
programs, I'd like to be on the safe side." 

"If you want to be safe, then forget the 
wisecracks and restrict your comments to 
assembler language." Jack rose and walked 
to the kitchen to begin dinner. The power 
supply pilot light watched him turn the hall 
corner. Silently, the cassettes began to move. 



"I've been assembling everything on your 
tape library," said computer as Jack re- 
turned to the shop. "This assembler language 
isn't half bad." 

"OK, sharp stuff. Let's see you try this." 
Jack placed a cassette into recorder one. 
"There's about 200 lines of assembler code 
on this tape, exercising all your instructions. 
I want to see how fast you can get through 
it. Ready...? GO!" 

The cassette in drive one turned as 
computer read in the first record. Jack 
started his stopwatch. A short time later, 
computer read record two. Time passed, and 
the time between reads grew and grew. Many 
minutes later, Jack began pacing the floor. 
Still later, he went out to make some coffee; 
his ears were straining to hear the clatter of 
the Teletype that would indicate the end of 
pass one. At last, Jack could wait no longer. 
He strode back to the computer and pressed 
the interrupt button. 

"But, Jack, I was almost done! Just a few 
more labels to find and I'd have finished it. 
What's your rush, anyway? I never saw so 
many labels before! I barely had enough 
memory for all that alphanumeric 

gobbledygook!" 

"Computer, your label searching method 
is abysmal! I could read an entire issue of 
BYTE in the time you waste hunting around 
in your symbol table. What can we do about 
it?" 

"Sorry, Jack, but I'm searching as fast as 
I can. I have to look entry by entry, so when 
the table fills I have a lot of looking to do. I 
can't use your binary search stuff here, since 
I don't have the symbol table ordered. Now, 
if you could guarantee that your labels 
would appear in alphabetic order, then ..." 

"No such luck, old buddy. That's a task 
you'll have to perform." 

"Jack, do you have any idea how long it 
would take me to insert new labels if I had 



58 



to resort the whole list every time? You 
think I'm slow now!" 

"Don't blow your fuses! I don't intend 
for you to spend your life sorting symbol 
tables. I've just read about this new tech- 
nique, and it sounds perfect for you. It's 
called 'hash coding.' " 

"If you had designed it, they'd probably 
call it the 'Irish stew' algorithm. Besides, you 
make enough of a hash of my programs 
already." 

"Hold on, you animated son of a sand 
pile! This is serious business. Will you just 
listen for a while?" 

"Why the slur on my silicate origins, 
Jack? I reserve the right to protest, but I'll 
hear you out." 

"Now . . . the basis of hash coding is to 
generate a random number based upon each 
label." 

"Jack, please! I am a computer, re- 
member! The only times I produce random 
output is when I'm broken. You're the one 
who sometimes behaves randomly!" 

"I really don't expect you to be random. 
I really mean 'pseudorandom.' I'll write an 
algorithm which takes the characters of a 
label and makes them into a number that 



"I've just read about this new technique, and it 
sounds perfect for you. It's called 'hash coding.' " 
said Jack enlightenedly. "If you designed it, they'd 
probably call it the 'Irish stew' algorithm," replied 
computer rebelliously. 



will be an address that could be anywhere in 
your symbol table space. It has a uniform 
probability of forming any address. Each 
label will have a unique place, and you'll be 
able to find it by hashing its name, instead 
of searching the whole table. The process 
only looks random. Actually, it's a fairly 
simple mapping from label to address in 
symbol table. Do you follow me, 
computer?" 

"Yes, but I see problems ahead. You can 
generate lots of labels, millions in fact. You 
can't expect me to have space for each one." 

"No, you'll have a limited symbol table 
space. We'll let it be as big as the memory 
left over after your assembler translating 
programs have been loaded." 

"But, Jack ... if that's true, then you'll 
have to let many different labels hash, as 



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"Yeh, and I'll put a fried egg on top! Hashing and 
rehashing doesn't seem at all obvious! I go running 
around memory chasing a plate of hash. When I find 
it, I have to see if the hash is done. If it isn't, I branch 
to a half baked program and loop until done." 



you call it, into the same symbol table 
address. I can't tolerate that." 

"Never fear! You'll know whether an 
address in the table is occupied or not. If it 
isn't, then the first label to hash to it will 
occupy it. If another label hashes to that 
occupied address, then you'll rehash the 
label to get a new address. Sooner or later 
you'll find an empty symbol table address to 
put that label in. The only time you'll need 
to search the whole table is if it is entirely 
full ... an unlikely occurrence. Remind me 
later to write you a rehash program. I've got 
a linear rehash algorithm in a book around 
here somewhere. At any rate, you can find 
your label in fewer hashes than you'd need 
searches. You store the whole label in the 
symbol table, so you can check the label you 
just hashed against the label you found at 
the hash address. You can use the compare 
routine I gave you for checking mnemonics. 
That way you'll be able to tell when you 
need to rehash. It really isn't very hard." 

"Yeh, and I'll put a fried egg on top! This 
doesn't seem at all obvious! I go running 
around memory chasing a plate of hash. 
When I find it, I have to see if the hash is 
done. If it isn't, I branch to a half baked 
program and loop until done." 

"Enough of that, computer. When you 
have the code, you'll find it rather a thrill to 
assemble programs in minutes instead of 
hours. I'll leave that long program in the 
reader. Try it again this evening. You'll like 
it!" 

"That's not very funny!" mumbled com- 
puter as Jack walked toward the kitchen. 
"I'll bet he's not cooking hash tonight!" 



"Bring on the big pro- 
grams ... Give me enough 
core and I'll assemble the 
Earth!" 



"You know, Jack, you're pretty smart for 
a human. That hash coding trick really 
works! I finally got it figured out, I think. 
Let me tell you how I do it." 

"After a compliment like that, how could 
I refuse you?" 

"Well, suppose I have to keep track of 
three character names, for instance. You tell 
me that I'll only need to store a maximum 
of 26 names, not the thousands that could 
be formed. I must invent a transformation 
that converts three character names into 



numbers in the range one to 26. For 
simplicity, I choose to take the first letter of 
the name as my first hash. Subsequent 
rehashes, if necessary, will use the second 
and third character. So, if you give me the 
names MEL, MOE, and MOA, I perform as 
follows: All three names hash first to address 
14. I put MEL into that slot, since it is 
processed first. When I hash MOE, I find 
that its hash address of 14 is already 
occupied. I rehash MOE based on the second 
character and place it into slot 16. Similarly, 
I will rehash MOA twice and eventually put 
it into slot 1." 

"Computer, you've got the right instincts, 
but your hashing algorithm isn't the best one 
to use. We humans have a tendency to use 
similar names, often a series of similarly 
spelled names. Remember my exam- 
ple... LINE1, LINE2, etc.? Your system 
would take too many hashes to work with 
names like those. You ought to use a hash 
that uses all of the characters in the name 
each time. Then it will appear more random, 
and will be less likely to hash similar names 
to the same address. If you read cassette 
one, you'll find such an algorithm. It's not 
very simple to describe, but you'll find it 
quite efficient to use." 

The room was silent, except for an 
occasional sound from the tape drives. Com- 
puter's lights blinked furiously for several 
minutes and then suddenly stopped. "OK, 
Jack, I've got it all memorized. Shall we try 
your test assembly again?" 

"Right away, old buddy. Your tapes all 
set? Fine ... on your mark, get set, GO!" 

A scant moment later, computer's Tele- 
type began typing its message at the end of 
pass one. Jack rewound the input tape and 
started pass two. "NO ERRORS" chortled 
the computer. "I'll bet that was fast enough 
even for you!" 

"It's a new world's record for Motorola 
assemblers! Take a rest, hero! You sound a 
bit winded." 

"No, Jack, just excited by all this speed. 
You can get me more memory now ... I'm 
ready for it. Bring on the big pro- 
grams . . . give me enough core and I'll as- 
semble the Earth!" 

"If I let you go on like this, you'll be 
giving out Tarzan yells and probably pop all 
your fuses. Good night, computer." 

"Good night, Jack" said computer, its 
voice trailing off as Jack flipped the power 
switch. The gleaming red eyes dimmed. 



"Don't get too upset, computer, but I've 
got more for you to learn." 



60 



"Computers don't have hearts, remember that. Don't 
confuse your clock with a pulse." 



"That's a good point. For now, let's just 
print the representation of the first character 
and I'll trust you to get the rest of the 
character string correctly." 

"I am heartened by your trust." 

"Computers don't have hearts, remember 
that. Don't confuse your clock with a 
pulse." 

"I'm duly chastised. Now let me guess 
your next request. You want to be able to 
name your programs. You always did like 
naming things." 

"That wasn't my next thought, but it's a 
good idea. Let's say that a NAM pseudo 
operation can assign a name to a program, 
and you'll label the listing with this name." 

"That was an easy one, Jack. Give me 
another simple one." 

"OK. How about a pseudo operation to 
skip to the top of the next page of the 
listing?" 

"No sooner said than done. Call it PAG?" 

"Fine. Now another easy one. I don't 
always need a complete assembly. Some- 
times I would rather you skip the listing, or 
the output object file, or pass two. I'll tell 
you what steps I want done in a pseudo 
operation called OPT. If I don't specifically 
specify an option, you'll assume I want it. 
Understand?" 

"I think so, Jack. Unless you tell me 
otherwise in an OPT command, I give you 
the works." 

"Fine. Just one more pseudo operation 
and we'll have it. I will want to be able to 
define constants in terms of other values. 
This is like the form constant operations, 
but the resulting value won't be in memory. 
You'll just keep the value in your symbol 
table ... on hand when I ask for it. When- 
ever you see the symbol, you'll insert the 
value I've defined it to have." 

"Your wish is my command! I will 
reserve the right to flag you if haven't 
defined all your symbols when I need them 
in pass two." 

"I wouldn't have it any other way. We 
can call this operation EQU, because it 
works like an "equals" sign. The operand 
may contain arithmetic and maybe other 
symbols and constants that will have defined 
values in pass two. The final result is the 
value of the pseudo operation. You'll store 
the value in your symbol table as though it 
were an address ... as two bytes. If the 



value works out to a single byte, then zero 
out the high order byte." 

"Fine, fine, Jack, now Jet me go back to 
running through my hash tables. I just love 
to run through a field of operation codes. It 
makes me feel warm all over." 

"If you feel warm, I'd better check things 
out." 

"No, Jack. Don't turn off the power! 
Please! NOOOooo ..." 



Note: Readers interested in 
using the Assembler Jack Built 
should contact Jack 
Hemenway at 151 Tremont 
St, Boston MA 021 1 1 . 



"You know, computer," said Jack as he 
strode into the shop from the kitchen, "the 
gang at the computer club was very in- 
terested in the assembly language that you 
and I have worked out. They'd like me to 
sell copies of it. How do you like that?" 

"I like it fine, so long as you copy the 
listings yourself and don't expect me to type 
them out hour after hour. Your wife will 
appreciate our making some money, espe- 
cially after all you've invested in me. 
And . . . then, maybe you'll bring me to a 
club meeting. I don't encounter much vari- 
ety here on your desk." 

"You're a little hard to travel with, you 
know. You aren't exactly a neat, tidy 
package." 

"And whose fault is that, Jack? I didn't 
build myself." 

"OK, OK... I'll tal<;e you out soon. 
Meanwhile, you've got to help me solve a 
slight problem. Most people who have small 
computers at home don't install much over 
four to eight kilobytes." 

"So what's the problem? My assembler 
programs fit easily into 8 K." 

"I know that, computer, but the problem 
is where the slice of memory is located in 
address space. If I'm going to sell our 
program, we've got to make it possible to 
load it into any sufficiently large memory 
slice. In a word, we've got to make our 
assembler relocatable. At the same time, we 
can make the output of the assembly process 
relocatable too. This will allow the as- 
sembled code to be loaded anywhere in 
memory. This will be a big help to people 
building up large programs from smaller 
segments. They can assemble a program one 
piece at a time." 

"So, I still don't see much problem. You, 
Jack, will just have to write a loader program 
that puts my assembler into the right place 
in memory. I'll do the rest. That loader 
should also work with my output code." 

"It is nearly that easy. I would like you 
to do one other thing, though." 

"I knew there would be a kicker to it! So 
what do you want now?" 



62 



"You never quit, do you Jack? OK, what 
is it this time?" 

"I'm going to teach you some new 
operations that I'd like to have." 

"Hold it, buddy. I've already got all the 
operations I can use. Besides, operations are 
part of my hardware, and I like my internal 
arrangements the way they are! No new 
operations, Jack!" 

"I'm not about to touch your little body, 
so don't worry. I plan to implement these 
new operations in your assembly language 
translation programs. They'll actually be 
'pseudo operations.' They'll be added to 
your mnemonic table, and they'll help us 
communicate. For instance, you need to 
know where the end of a program is, right? 
How else can you know when to start pass 
two?" 

"That's pretty obvious, Jack. So you're 
going to define some operation that really 
means 'stop pass one and start pass two.' 
Probably call it END." 

"Well, that's one pseudo operation done. 
Now ... I often want to set aside areas of 
memory for certain purposes. I'll be storing 
stuff into those areas sometime during a 
program; but right now, I just want to tell 
you that space is to be reserved. I want you 
to recognize the pseudo operation RMB as a 
note to reserve the number of bytes that 
appear in the operand." 

"I assume you're going to provide sub- 
routines for all this, Jack." 

"Of course, computerized bookkeeper. 
Where was I? Oh, yes, I'll want to be able to 
form constants in memory. Let's let FCB 
indicate the formation of a byte of data 
initialized to the value of the operand. 
Similarly, FDB will indicate a double byte of 
data to be initialized to the value of the 
operand. These pseudo operations will have 
labels, so that I can refer to the value I've 
had you form in these locations." 

"They're like immediate operands, 
right?" 

"Right, computer. You'll perform all the 
steps necessary to evaluate the operand field, 
and that is the immediate value to store in 
that location. I also want a pseudo operation 
to form character strings in ASCII code. 
We'll call it FCC. It works like the other 
form constant operations, except that the 
operand will be enclosed in single quotation 
marks and will be converted into its ASCII 
representation in memory." 

"One problem with that, Jack. I don't 
have room to print out long character strings 
in the assembly listing. Do you want me to 
use extra lines, or will that be too 
confusing?" 



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"Well, computer, as you can probably 
recognize, some addresses in a program can 
be relocated and others can't. If an address is 
defined relative only to the start of the 
program, then it can be relocated with the 
rest of the program. If it is defined abso- 
lutely, like by equating a label to a hex 
constant, then it isn't relocatable. Some 
computations involving addresses will give 
relocatable results, others won't. I want you 
to label all relocatable addresses when you 
print a listing. There's enough space in the 
listing format for a letter R after the 
operand field of each instruction containing 
a relocatable address." 

"I have some questions, Jack. First, I 
have an addressing mode which requires 
addresses to be in the first 256 bytes of 
memory. How do I know when to use this 
mode? Second, how do I figure out whether 
the result of a computation is relocatable?" 

"We'll make the following rules. If the 
address of the operand is relocatable, then 
use extended addressing mode rather than 
direct mode, regardless of the relative ad- 
dress of the operand. In other words, if the 
program writer wants you to use direct 
addressing, he's going to have to specifically 
ask for it. As another general rule, a com- 
putation will be relocatable if it contains an 
odd number of relocatable terms. A com- 
putation with a single relocatable term and 
constants is clearly still relocatable. The 
difference between two relocatable terms is 
not relocatable. One relocatable term di- 
vided by another is not relocatable. There 
are cases where this simple algorithm gives 
rather meaningless results, but works prop- 
erly in most useful applications I can think 
of. Again, we'll let the programmer force the 
issue if he wants to do so." 

"As you like. That does it, Jack? As- 
sembler is finished? I can get some sleep 
now?" 

"Sure, computer. I've got some desk 
work to do before we start selling the 
assembler. Unfortunately, you can't help me 
do this work. I've got to write documenta- 
tion on the program, flow charts and instruc- 
tion manuals. Yech! The thought of writing 
all that stuff is disgusting." 

"Why don't you have one of your friends 
from the computer club do a write-up for 
BYTE?" 

"That's a good idea. I'll get on it." 

Jack shifted his chair and began to sketch 
flow charts of the assembler routines. Com- 
puter settled down to read about a new 
BASIC interpreter it had found in the 
program library. Jack was so busy, he left 
the power on for days." 



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63 



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Technology 

6200-SHollis Street w * 
Emeryville, CA 94606 



Build a TV Readout Device 
for Your Microprocessor 



Dr Robert Suding 

Research Director, The Digital Group Inc 

PO Box 6528 

Denver CO 80206 

A television set readout for your micro- 
processor has many attractive advantages. 
The TV readout is vastly faster, quieter, and 
even lighter, than the usual Teletype based 
design. Since it is an electronic rather than 
mechanical device, less service and main- 
tenance are required. Much more data may 
be contained on a television screen than on 
front panel readouts. 

The precise design of the television 
driving circuitry (interface) can take on a 
considerable number of forms. Some con- 
siderations are: 

• Number of horizontal characters. 

• Number of vertical characters. 

• Upper case only, or upper and lower 
case text. 

• Character generation format: 

row or column scan. 

5x7 dot matrix, 7x9 dot matrix 

or? 

• Alphanumeric only, or alphanumeric 
and graphic formats? 

• Converted home TV set or commercial 
TV monitor? 

• Separate TV buffer memory or TV 
buffer shared with main memory? 

• Shift registers for memory, or pro- 
grammable RAM? 

• Multiple video pages or single display? 

• Interlaced scan or non interlaced? 

• Hardware or software cursor, or no 
cursor? 

Rather extensive list, isn't it? Understand- 
ably, a large number of designs have ap- 
peared recently, and many more will be 
seen. Every design has some advantages, 
some disadvantages. 

The 5x7 dot television display circuit in 



the June 1976 BYTE [page 16] is an 
example of a number of the above design 
alternatives. The 5x7 dot 251 3 is a rugged, 
low cost character generator. The MM5320 
is a fairly easy way to generate an interlaced 
signal. Programmable random access mem- 
ory provides a random and faster screen 
update capability compared to the shift 
register "TV typewriters" of a few years ago. 

Major Features 

The television display design shown in 
this article has several major departures from 
previously published designs. The June 1976 
BYTE article on "A Systems Approach to a 
Personal Microprocessor" [page 32] stresses 
the need to keep various system elements 
independent in order to avoid unnecessary 
obsolescence. By using a simple parallel 
interface and making refresh memory part of 
the design, this television display achieves 
independence from a particular computer 
and bus design. This same display is also 
useful in such items as terminals, TV type- 
writers, and large computers. 

A Motorola MCM6571 L character gen- 
erator is used as the heart of the Digital 
Group as well as several other video display 
systems. This character generator provides a 
7x9 dot matrix character with automatic 
character shift for lower case characters such 
as g,j,y, etc, which extend below the base 
line, making an effective 7x13 dot matrix. 

Thirty-two characters per line by 16 lines 
give a total of 512 characters on the screen. 
Endless arguments can result when screen 
formats arise. The 32x16 format was 
chosen to achieve the clearest and simplest 
(hence lowest cost) system. The more char- 
acters per line, the more television band- 
width is required. This system requires a TV 
monitor with better than 6 MHz bandwidth. 
A system with 64 characters per line would 
require a 12 MHz monitor, etc. Since the 
system was designed to minimize costs, a 



66 




Figure 1 : Memory and write address counter logic for the TV readout design. 
The inputs to this circuit are at the left, labelled DO to D7 corresponding to 
the data lines of a typical latched output data port. The connections to fig- 
ure 2 include DO and D7, memory outputs CO to C6, and video timing chain 
address lines AO to A8. 



+5 POWER SUPPLY PINS 


Number 


Type 


+5V 


GND 


IC1 


2102 


10 


9 


IC2 


2102 


10 


9 


IC3 


2102 


10 


9 


IC4 


2102 


10 


9 


IC5 


2102 


10 


9 


IC6 


2102 


10 


9 


IC7 


2102 


10 


9 


IC8 


74157 


16 


8 


IC9 


74193 


16 


8 


IC10 


74193 


16 


8 


IC11 


7404 


14 


7 


IC12 


74193 


16 


8 


IC13 


7400 


14 


7 


IC14 


7400 


14 


7 


IC15 


74157 


16 


8 


IC16 


74193 


16 


8 


IC17 


74193 


H6 


8 


IC18 


7410 


14 


7 


IC19 


7404 


14 


7 


IC20 


7420 


14 


7 


IC21 


74193 


16 


8 


IC22 


7430 


14 


7 


IC23 


74123 


16 


8 


IC24 


74193 


16 


8 


IC25 


7430 


14 


7 


IC26 


7401 


14 


7 


IC27 


74L00 


14 


7 


IC28 


74157 


16 


8 


IC29 


74193 


16 


8 


IC30 


MCM6571L 


2 


13 


IC31 


74165 


16 


8 


IC32 


74193 


16 


8 



67 



Figure 2: Character generation, composite video output and video timing 
chain logic for the TV readout design. The output of the TV readout is the 
composite video signal which drives a monitor or modified standard television 
set through a coaxial cable. The character generation logic consists of a read 
only memory, IC30, to translate character patterns into horizontal rows of 
dots, and the shift register, IC31, which sequences the bit by bit output of 
the row of dots. The video timing chain is a series of counters driven by the 
5.990 MHz crystal, which cycles through the memory section of figure 1 and 
controls operation of the display. 



A Note About Construction 

The circuit shown in figures 1 and 2 is 
complete, and can be constructed in any well 
equipped home hardware laboratory using point to 
point soldering, home brew printed circuits. Vector 
wiring pencils, or wire wrap as an interconnection 
technique. 

For those who wish to take advantage of 
construction using a circuit board and a complete 
set of electronic parts, Dr Suding'sTV readout and 
the cassette interface described in his article on 
page 46 of July BYTE are available in a combined 
kit form for $130, postpaid in the USA. Contact 
the Digital Group Inc, PO Box 6528, Denver CO 
80206, for information on this product. 

For home brewers, the only part which might 
be difficult to find in surplus markets is the 
Motorola MCM6517L character generator chip. 
This package is available over the counter at many 
major electronics trade distributors. If you are 
unable to locate the MCM6517L from such a 
source, the part can be purchased for $20 postpaid 
in the USA from the Digital Group. 



POWER 
CONDITIONING 



5V 



+ I2V 
A 




luF ftl 



Zl 

5V 

ZENER 



01 



DWN LOAD CLR 

lp IC32 s 

74 1 93 



LOAD CLR 
DWN |C|7 

UP 74 1 93 

0A 08 0C 0D 



LOAD CLR 

DWN |(;2| 

74I93 



IC24 
74 1 93 



DWN LOAD CLR 

ICIO 
up 74 1 93 

0A QB OC 0D 



LOAD CLR 

DWN | C | 2 

74 1 93 




68 



home black and white television set can be 
easily modified [page 20, October 1975 
BYTE] and will satisfactorily meet the 
6 MHz requirement. Sixteen rows of char- 
acters allow use of a non-interlaced sync 
system for lower cost. My own preferred TV 
display formats are either a 32 x 16 char- 
acter system or the 80 x 24 character for- 
mat. However, the 80 horizontal characters 
will require an expensive monitor to achieve 
the 15 MHz TV bandwidth and critical 
corner focus requirements. 

The character memory can be of several 
formats, but this system uses a self con- 
tained programmable memory buffer which 
is loaded sequentially from the driving 8 bit 
output port of the microprocessor, or an 
ASCII keyboard. Some systems permit data 
readback from the TV readout system, but a 
greater cost is involved, and a mirror image 
buffer in the computer's programmable 
memory will produce the same result. Use of 
programmable random access memory in the 
TV readout permits very fast loadings, as 
fast as the system can output data. The 
typical update time for a total of 512 
characters is under 5 ms. How far under 
5 ms depends on the driving software and 
microprocessor used. 

Cursors and cursor control may be per- 
formed in hardware or software. The ap- 
proach of this system is to use software for 
the most part, which results in lower cost 
hardware. Cursor inserting subroutines are 
then used as needed. 

So much for system design alternatives. 

TV Readout Description 

This TV readout consists of five inter- 
acting sections. They are memory, character 
generation, composite video output, video 
timing chain, and write address counter. The 
memory section (figure 1 ) consists of seven 
2102A-2 or faster 1 K memories. Only one 
half of each memory is used, giving a 
possible storage of 512 seven bit ASCII 
characters. The microprocessor, keyboard, 
or some attached circuit writes the char- 
acters one by one into the 2102s, and then 
the TV readout continuously displays these 
characters until either more characters are 
entered, or the circuit is turned off. 

The character generation circuit (see 
figure 2) consists of two integrated circuits, 
the MCM6571L character generator, IC30, 
and the 74165 shift register used to convert 
from parallel to serial. The 6571 takes the 
seven bit ASCII character coming from the 
memories and outputs 7 dots making up a 
character row for each of 13 potential rows 
making up each character. The 74165 loads 



all 7 dots into its internal memory, and then 
outputs these dots one at a time for serial 
transmission to a TV set. For more informa- 
tion on TV character generators, I would 
suggest reading an excellent article by Don 
Lancaster in June 1974 Radio Electronics 
[pages 48-52], or the June 1976 BYTE 
magazine article by C W Gantt [page 16] . 

The video output section uses a 7401 
open collector NAND gate and a driver 
transistor to produce a low impedance com- 
posite video signal. The output is around 3 V 
peak to peak with about a 1/2 V horizontal 
and vertical sync and blanking pedestal. 

The read clock (see figure 2) is the source 
of master control for the various sections. 
Starting from an initial frequency of 
5.990 MHz, a countdown chain of three 
74193s (ICs32, 17, and 21) produce an 8 ms 
horizontal sync when gated by IC11a, 
IC20a, IC18b, IC1 3c and IC1 3d. A 41ms 
horizontal blanking circuit prevents loss of 
characters at the edges of the screen, and is 
produced by the gating action of IC14, 
IC11c, ICIIf and IC13a. The resultant hori- 
zontal frequency is 15,598 Hz, somewhat 
lower than the standard 1 5,750 Hz, but 
usually only requires trimming horizontal 
hold slightly, if at all. 

The vertical countdown chain uses three 
more 74193s (ICs24, 10 and 12) to obtain a 
final vertical frequency of 60 Hz, the same 
frequency as the AC line to avoid hum roll 
and wobble problems on low cost televi- 
sions. IC19b, IC19c, IC19d and IC25 pro- 
duce an 820 jus vertical sync pulse, IC18a 
and IC19e detect state 20 of IC10 and IC12, 
counting lines to 19 and giving four line 
periods for vertical retrace. The inverter 
IC19f produces a 3.5 ms vertical blanking 



Photo 1: A test demon- 
stration of Dr Suding's TV 
readout, shown in schema- 
tic form as figures 1 and 2. 
The test pattern consists 
of the four lines in the 
center which cycle 
through the possible bi- 
nary combinations of 
characters. The differences 
in line width between the 
top line and the other lines 
are caused by non-linear- 
ities in the monitor used 
for this photograph. 



69 



pulse during states 16 to 19 of the counter 
ICIOand IC12. 

As if these operations weren't enough, 
part of the video timing chain, counter IC24, 
tells which of the 13 lines in a character is 
being currently accessed. The counter IC32 
keeps track of shifting and loads the 74165 
when the row of 7 dots is available from the 
6571. The 5.990 MHz signal then shifts out 
8 dot periods (the 8th one is a horizontal 
space between characters) before the next 
dot load command occurs. All of these 



timings are very critical during the design 
phase; but since the circuit is digital, the 
builder should have no problems, since no 
adjustments are needed. The video timing 
chain counters develop a 9 bit address that 
controls which of 512 characters is currently 
being presented to the 6571 for dot en- 
coding. This is routed to memory through 
74157 multiplexors IC15, IC28 and IC8 
except during write clock time. 

I thought you'd never ask about the write 
clock. Well, it controls the entry of the 



Figure 3: 



Check Out Notes 

The TV readout should be assembled according 
to your preferences (see "A Note About Construc- 
tion") using sockets for all integrated circuits. 
These notes suggest a procedure for orderly testing 
of the new TV readout. 

1. Power supply. Start checkout after all wiring 
has been completed, but before any integrated 
circuits have been inserted into sockets. Measure 
the resistance between ground and the other 
voltage supply pins. A very low resistance indicates 
a bad bypass capacitor, a solder bridge, or some 
other forn of short circuit between the supply 
voltage and ground. 

2. TTL integrated circuits. Insert all the in- 
tegrated circuits of the TV readout except the 
memories (2102s, IC1 to IC7) and the character 
generator (MCM6517, IC30). Measure the resis- 
tance between the ground and the +5 V supply pin, 
noting its value; reverse the ohmmeter leads and 
remeasure. A shorted reading in either direction 
indicates a bad integrated circuit, and nearly equal 
readings in both directions indicates that at least 
one integrated circuit has been plugged in in 
reverse. 

3. Initial power up. Temporarily ground the most 
significant bit input pin (D7 in figure 1), and 
connect the video output to a commercial TV 
monitor, or a TV set which has been modified to 
act as a monitor. Turn on the +5 V power. You 
should see 32 white vertical columns on the screen. 
(Refer to the "Diagnosis of Ailing Readouts", 
section 2, if this does not happen.) Turn off +5 V 
power. 

Connect up the +12V and -12 V power sup- 
plies, then turn on all power again. Verify the 
proper voltages on the MCM6517L socket, IC30: 
Pin 1 should have -5 V, pin 2 should have +5 V and 
pin 3 should have +12 V. Turn off power again. 

4. Now plug in the MOS parts: The seven 2102 
memory integrated circuits and the MCM6517 
character generator read only memory. (The tem- 
porary ground jumper for the D7 input, and the 
video monitor output are still attached.) This time, 
when power is turned on, you should see a random 
display of 512 characters on the screen. The actual 
character at each location is determined by the 
chance power on initialization of each bit location, 
and cannot be predicted in advance. 

5. Testing: Complete testing is now possible 
under computer control or by using a breadboard 
input device. If you use microprocessor control. 




TO D7 STROBE 
INPUT 



7413 SCHMITT TRIGGER 
PIN 7-GND 
PIN I4-+5V 



/77 



A test setup for manual verification of the 
display. The Schmitt trigger integrated cir- 
cuit, a 7413 NAND function, has an RC 
feedback network to cause oscillations. This 
logic oscillator is used to drive the strobe 
input continuously, so that memory will be 
filled with a constant character pattern if 
that pattern's ASCII code is presented on 
input pins DO to D6. 

simply wire the inputs to the TV readout to an 
8 bit output port, load the software of listing 1 (if 
you have an 8080 or Z-80; write equivalent 
programs for other processors if necessary), and 
write some simple programs to generate known 
data and load that data into the display. 

If it is desired to test the TV display without a 
microprocessor, the oscillator of figure 3 can be 
used to drive the input strobe pin, D7. Then 
temporarily tie all the other data pins to the +5 V 
supply through a 1 k resistor. Verification of the 
operation of the display can be obtained by 
grounding bits DO through D6 of the input (the 1 k 
pullup resistors protect the power supply). The 
following table gives the characters which should 
fill the screen for each case: 



Pin to 




Octal 


Ground 


Character 


Code 


DO 


'V 


376 


D1 


} 


375 


D2 


{ 
w 


373 


D3 


367 


D4 





357 


D5 




337 (underscore) 


D6 


? 


277 



70 



characters from your external source into 
the 2102 memory bank. Several alternatives 
in character entry are possible, yet give the 
user a very capable unit, particularly when 
using a microprocessor, or even mini, midi, 
or maxi processors. 

A sequential entry system is utilized. A 
home reset control signal (denoted "■") is de- 



veloped by IC22 when it detects all of the 8 
input lines high ("1"). The write address 
counter of IC1 6, IC29 and IC9 is then preset 
so that the next character to be entered will 
result in its being displayed as the top 
leftmost character on the screen. The second 
character will be viewed to the right of the 
first, . . . until on the 33rd character a new 



Table 1 : Character graphics, octal codes and binary codes for the TV readout. 



Char 



X 



t 
z 

blank 
I 

# 
$ 
% 
& 

( 

) 

+ 



> 



Octal 



Binary* 



Char 



Octal 



Binary* 



200 


10 000 000 


@ 


201 


10 000 001 


A 


202 


10 000 010 


B 


203 


10 000 011 


c 


204 


10 000 100 


D 


205 


10 000 101 


E 


206 


1 000 1 1 


F 


207 


1 000 1 1 1 


G 


210 


10 001 000 


H 


211 


10 001 001 


I 


212 


10 001 010 


J 


213 


10 001 011 


K 


214 


10 001 100 


L 


215 


10 001 101 


M 


216 


10 001 110 


N 


217 


10001 111 





220 


10 010 000 


p 


221 


10 010 001 


Q 


222 


10010010 


R 


223 


10010011 


s 


224 


10010 100 


T 


225 


10010 101 


u 


226 


10010 110 


V 


227 


10010 111 


w 


230 


10 011 000 


X 


231 


10 011 001 


Y 


232 


10011 010 


z 


233 


10011 011 


[ 


234 


10 011 100 


\ 


235 


10011 101 


] 


236 


10011 110 


1—1 


237 


10011 111 


— 


240 


10 100 000 


1 


241 


1 1 00 001 


a 


242 


10 100 010 


b 


243 


10 100 011 


c 


244 


1 1 00 1 00 


d 


245 


10 100 101 


e 


246 


1 1 00 1 1 


f 


247 


1 1 00 1 1 1 


9 


250 


10 101 000 


h 


251 


10 101 001 


i 


252 


10101 010 


i 


253 


10 101 011 


k 


254 


10 101 100 


1 


255 


10 101 101 


m 


256 


10 101 110 


n 


257 


10 101 111 





260 


10 110000 


P 


261 


10 110 001 


q 


262 


10 110010 


r 


263 


10 110011 


s 


264 


10110 100 


t 


265 


10 110 101 


u 


266 


10 110 110 


V 


267 


10110 111 


w 


270 


10 111 000 


X 


271 


10 111 001 


V 


272 


10111 010 


z 


273 


10 111 011 


{ 
} 


274 


10 111 100 


275 


10 111 101 


276 


10 111 110 


~ 


277 


10 111 111 


"Hor 



300 


1 1 000 000 


301 


11 000 001 


302 


11 000 010 


303 


11 000 011 


304 


1 1 000 1 00 


305 


1 1 000 1 01 


306 


11 000 110 


307 


1 1 000 1 1 1 


310 


11 001 000 


311 


1 1 001 001 


312 


11 001 010 


313 


11 001 011 


314 


1 1 00.1 1 00 


315 


11 001 101 


316 


11 001 110 


317 


11 001 111 


320 


11 010 000 


321 


11 010 001 


322 


11 010010 


323 


11 010 011 


324 


11 010 100 


325 


11 010 101 


326 


11 010 110 


327 


11 010 111 


330 


1 1 01 1 000 


331 


1 1 01 1 001 


332 


11 011 010 


333 


11 011 011 


334 


11 011 100 


335 


11 011 101 


336 


11 011 110 


337 


11 011 111 


340 


11 100 000 


341 


11 100 001 


342 


11 100 010 


343 


11 100 011 


344 


11 100 100 


345 


11 100 101 


346 


11 100 110 


347 


11 100 111 


350 


11 101 000 


351 


11 101 001 


352 


11 101 010 


353 


11 101 011 


354 


11 101 100 


355 


11 101 101 


356 


11 101 110 


357 


11 101 111 


360 


11 110 000 


361 


11 110 001 


362 


11 110010 


363 


11 110011 


364 


11 110 100 


365 


11 110 101 


366 


11 110 110 


367 


11 110 111 


370 


11 111 000 


371 


11 111 001 


372 


11 111 010 


373 


11 111 011 


374 


11 111 100 


375 


11 111 101 


376 


11 111 110 


377 


11 111 111 



*The low order 7 bits of the binary representation map into the ASCI I graphics where such graphics are defined. 
The high order bit is always a "1" value to act as a strobe in the software of TVOUT shown in listing 1. 



71 



Diagnosis of Ailing Readouts 

1 . Troubles — General 

• One of the more difficult troubles to find is 
an IC pin which was bent under the inte- 
grated circuit when it was inserted. Any 
unusual pressure when inserting an inte- 
grated circuit should be investigated. 

• Check continuity. Your wiring should be 
correct. If soldering is used, as in printed 
circuit assembly, check to make sure all 
joints are in good shape. 

• When troubleshooting with an oscilloscope 
probe, measure from the fop side of the 
integrated circuit, not the bottom, to elimi- 
nate the possibility of being misled by a pin 
which is bent under or a defective socket. 

• Before ever plugging in any integrated 
circuits, always measure the voltages at the 
terminals of the display board and at the 
power pins of the more expensive integrated 
circuits, like the MCM6571 . 

• When handling integrated circuits, avoid 
static charges. Run your house humidity 
high, and ground yourself by touching a 
grounded chassis before touching the inte- 
grated circuits. 

2. When initially checking out, if no white 
columns appear on the screen at step 3, the 
following may be a cause of the problem. 

• Bad connection between TV output con- 
nector pin and TV. 

• Temporary jumper from input D7 pin to 
ground not connected. 

• Crystal not oscillating. Check for pulses at 
pin 1 of IC27. 

• Horizontal countdown chain defective. 
Successively measure output at pin 3 of 
IC32, IC17 and IC21. Each should be 
progressively lower in frequency. 

• Vertical countdown chain defective. As 
above, but measure pin 3 of IC24, IC10 and 
IC12. 

• Defective video mixer. Look for pulses at 
pinsl and 13 or IC26. 

3. Initial checkout pattern (step 3) is poorly 
defined or lacking synchronization. In this case the 
following comments might apply. 

• TV could be overloaded by the = 3 V of 
video. Cut the level by adding a series 
resistor of 10 ohms to see if sync and video 
stabilize. 

• Check for horizontal and vertical sync and 
blanking pulse at connector pin 1 6. A 75 ohm 
load should be attached. The pattern should 
look like this: 




If horizontal sync is defective, check 

IC11, IC20, IC18and IC13. 

If vertical sync is defective, check IC19 

and IC25. 

If horizontal blanking is defective, check 

IC11, IC13and IC14. 

If vertical blanking is defective, check 

IC19. 



4. No characters at step 4 of the checkout 
procedure. Look for: 

• Missing voltages at the MCM6571 (IC30). 

• Defective character generator. 

• Defective 74165 (IC31). 

• Defective logic signals to and from IC30 and 
IC31. All inputs and outputs should be 
pulsing at valid TTL levels (0 to 0.8 V = 
low; 2 to 5 V = high). 

5. Wrong character(s) in display when driving 
from computer or manual testing of step 5 in 
checkout. 

• Miswired or misjumpered input. 

• Defective memory IC. Note the bit dif- 
ference between the intended character. IC1 
is the memory for the Least Significant Bit 
(LSB) of the character . . .and IC7 is the 
Most Significant Bit's (MSB) memory. 

• Defective 741 57(s), IC8, IC15and IC28. 

6. "Twinkling" characters on TV. The source of 
this problem could be: 

• Slow memories. 650 ns or faster 21 02s must 
be used. 

• Overheated memories. Access times increase 
with heat. 

• Wrong pulse levels at pin 1 of 74165 (IC31). 
A base level of about 2.5 V with short 
positive and negative going spikes should be 
seen. 

• Defective character generator, IC30. 

• Incorrect timing components on 74123, 
IC23. 

7. Won't write characters into memory of TV 
readout. Look for: 

• Missing strobe pulse, or continuous level on 
D7 input. 

• No write pulse from 74123. Measure at pin 
12 of IC23, looking for an = 600 ns nega- 
tive going pulse. Connecting the D7 input to 
a s 50 kHz TTL clock will permit viewing 
on lower cost oscilloscopes. 

• Write clock not toggling. With above tem- 
porary oscillator inputting to D7, look for 
pulses at pin 3 of IC16, IC29 and IC9. 

• Defective memory address multiplexers, 
IC15, IC28and IC8. 

8. Extraneous characters can be caused by: 

• Noise on the input lines to the memory, 
particularly on the D7 line. A 220 pF 
condenser (C4) is used on D7 to suppress 
most noise sources. More or larger con- 
densers may be required in extreme cases. 
This trouble often shows up as an a appear- 
ing on the screen when another port is 
addressed. 

• Data sent to the TV character generator 
faster than it can handle. Data must be valid 
for 1.5 us following the rise of D7 strobe. 
Faster data rates can be handled by reducing 
the value of the condensers in the 74123 
write strobe singleshot. Alternatively, a data 
hold loop in your program, consisting of 
NOP instructions, can slow the data output 
to the readout. 

• Defective or slow memories. Look at the bit 
pattern of the extraneous character to deter- 
mine if a single memory is bad in a single or 
several data locations. 

• More bypassing required. Power supply 
conditioning is shown in figure 2. Look at 
the power supply with a high speed 
scope — if excessive voltage glitches are pres- 
ent, add capacitance. 



72 



line appears, displaying the 33rd character. 
Up to 512 characters are thus sequentially 
entered and displayed. If a 513th and 
following characters are entered, the address 
wraps around so that an overwrite condition 
results: New characters start appearing at the 
top left corner of the screen. The display 
address may be reset to the home position at 
any time. Screen erase is accomplished either 
by loading 512 or more ASCII "spaces" 
(octal 240) followed by the home reset 
(octal 377), or by issuing the home reset 
followed by exactly 512 ASCII spaces, the 
latter being preferable. 

Memory writing occurs when the MSB 
goes high. The memory address multiplexors 
(IC15, IC28, and IC8) then use the write 
address counter to control the memory 
address lines, interrupting normal display 
activity. 600 ns later, a 600 ns strobe pulse 
writes the new character into memory. 

An excellent idea was suggested by Phil 
Mork in the Digital Group Clearinghouse to 
utilize a parallel logic path to step the write 
address counter without writing a character. 
Using a cycle of 511 write address steps, a 
blank, 511 write address steps and a non- 
blank character, a blinking "pseudo cursor" 
effect is obtained without the usual expense 
of a number of comparators. This software 
"blink" may be easily implemented with a 
final result indistinguishable from a hard- 
ware cursor. The write address stepping logic 
consists of IC19a and IC27d which detect 
the presence of a "1" in the least significant 
bit while the most significant bit is held 
low. This toggles the write address counter 
without firing the 74123 write strobe 
(IC23b). Disable the "pseudo cursor" when 
using a direct keyboard input. Do this by 
disconnecting pin 12 of IC27 from IC19, 
and tying pin 1 2 to +5 V (logical 1 ). 

8080/Z80 Driving Software 

This television display can be driven by a 
microprocessor's 8 bit output port. In the 
Digital Group systems, we use port for 
this function. Listing 1 shows code for the 
routines CLEARTV, SPACE, and TVOUT to 
show how the software drivers are designed. 

The main subroutine is labeled TVOUT 
and is located at <0> 372. The programmer 
merely loads the A register with one of the 
characters from the list in table 1 and calls 
the TVOUT subroutine. The codes in table 1 
include all the standard upper and lower case 
ASCII codes, but have the high order bit of 
an 8 bit word set to "1". For those 
characters in table 1 which have ASCII 
graphics, subtracting 2 from the leftmost 
digit will give the equivalent 7 bit ASCII 



Split 














Octal 














Address 


Octal Coda 


Label 


Op. 


Operand 


<0> 343 


076 


377 




CLEARTV 


MVI 


A.377 


<0> 345 


315 


372 


<0> 




CALL 


TVOUT 


<0> 350 


006 


000 






MVI 


B.O 


<0> 352 


016 


002 






MVI 


C.2 


<0> 354 


315 


370 


<0> 


CLEAR 


CALL 


SPACE 


<0> 357 


015 








DCR 


c 


<0> 360 


302 


354 


<0> 




JNZ 


CLEAR 


<0> 363 


005 








DCR 


B 


<0> 364 


302 


354 


<0> 




JNZ 


CLEAR 


<0> 367 


311 






, 


■RET 




<0> 370 


076 


240 




SPACE 


MVI 


A.240 


<0> 372 


323 


000 




TVOUT 


OUT 





<0> 374 


257 








XRA 


A 


<0> 375 


323 


000 






OUT 





<0> 377 


311 








RET 




Entry points 















Listing I : Utility software for driving the TV readout with an 8080 or Z80 
system. This listing gives the CLEARTV, SPACE and TVOUT functions, a 
total of 28 bytes. The CLEARTV operation simply homes the display, then 
writes 512 spaces leaving a blank screen and the write address counter 
pointing to the upper left corner of the screen. The SPACE subroutine simply 
loads a space code into the accumulator (see table I) then falls through into 
TVOUT. TVOUT simply outputs the value in the accumulator, then clears 
the accumulator and outputs all zeros so that the write strobe (D7) is turned 
off completing the write operation. This routine assumes a latched output 
port. 



Commentary 

A := ' ■' [set up home reset character] ; 
write character [resets write address] ; 

)BC : = 2000 (set loop count to split 
octal equivalent of 51 2] ; 

write one space on screen; 
C := C— 1 [low order count] ; 
if not C = then reiterate the loop; 
B '.- B — 1 [high order count] ; 
if not B = then reiterate the loop; 
return with screen clear, write address 
counter pointing to home position; 
A := ' ' [load one blank character code] ; 
(port 01 := A; 

A :■ [turns off strobe pulse in bit 7] ; 
(port 0) := A; 
return from SPACE or TVOUT; 



CLEARTV: Called with no parameters when TV display screen is to be cleared completely and left in 

the "home" (upper left) position. Uses registers A, B and C 
SPACE: Called when a space (ASCII 040, 240 from table 11 is to be sent to the TV display. 

Uses register A. 
TVOUT: Utility output routine to transfer contents of A (high order bit assumed "1") to the TV display 

and increment the write address counter. Uses register A as input parameter, destroys its value 

leaving 0. 



code (with the high order eighth bit assumed 
to be zero). 

The instruction at <0> 370 will load the 
"space" character for you, so to get a space 
on the screen, merely call SPACE at address 
<0> 370. 

Before attempting to write any character 
on the screen, the user must know where on 
the screen the character will appear. A third 
included subroutine starting at <0> 343 
called CLEARTV will reset the write address 
counter to the home position and clear the 
512 character screen. The next character 
entered after this subroutine will appear at 
the top leftmost position on the screen. 

Conclusion 

This television display design provides a 
versatile and essentially self contained circuit 
to provide the key output device of a small 
and inexpensive computer system. It can be 
built from scratch in the typical experimen- 
ter's laboratory or from a kit provided by 
Digital Group. Due to its use of an extended 
character set with 127 symbols including 
upper and lower case, special characters and 
Greek, the display will prove quite useful in 
a variety of applications." 



73 




BOOK REVIEW 



Scelbi's Galaxy Game for the 8008/8080 by 
Robert Findley. Published by Scelbi Com- 
puter Consulting Inc, 1322 Rear — Boston 
Post Rd, Milford CT 06460, 1976. $14.95. 



At last, one of the most enjoyable and 
widely played computer games — Space 
War - becomes available to the 8008/8080 
microprocessor user with the publication of 
Scelbi's Galaxy Game for the 8008/8080. 

Running in 4 K programmable memory, 
the Galaxy program presented in the book 
embodies all of the major commands and 
principles of the familar BASIC or FOR- 
TRAN game "Star Trek." Through an ASCII 
keyboard, the operator commands the 
Federation starship to move throughout the 
galaxy and destroy a certain number of alien 
ships. Available at the captain's disposal are 
control of the starship's course and speed, 
both short and long range scanner displays, 
photon torpedoes, phasors, and protective 
shields. Scattered throughout the 64 quad- 
rants, each composed of 64 sectors, are stars, 
friendly space stations, and alien ships. 
Through the use of a random number 
generator, each Galaxy game is different 
and, I must say, challenging. 

The 169 page book is divided into seven 
chapters plus a brief introduction. Chapter 1 
details the operation of the game and 
explains the various commands along with 
their related warning and prompting mes- 
sages printed on the operator's Teletype 
video display. Chapter 2 assists the user in 
developing specific input and output rou- 
tines to tailor the software to a particular 
system. Chapter 3 explains how data is 
stored within the program. Chapter 4 con- 
tains a well documented explanation of the 
source code of the various subroutines and 
main program with frequent flow charts. 
Chapters 5 and 6, respectively, present the 
8008 and 8080 assembled object code. 



Finally, Chapter 7 presents a sample run of 
the program with helpful comments. 

After studying the source code for some 
time and admiring the efficient means 
chosen for storing a large amount of data, 
such as the location of the starship, the stars, 
alien ships, and space stations within the 
current quadrant, I entered without modifi- 
cation the object code of Chapter 5 into my 
8008 based machine, added my own input 
and output routines for keyboard and 
TVT-I, and proceeded to run the program. 
After correcting several of my own entry 
errors, Galaxy appeared to run properly, 
offering much enjoyment to an experienced 
Space War enthusiast as well as to complete 
novices. Though Galaxy does lack some of 
the bells and whistles of the FORTRAN 
versions, it is excellent for a 4 K micro- 
computer version. What surprised me was 
that even on the 8008, its speed of execu- 
tion was quite good. 

So far, I have only a few critical com- 
ments, all relating to initial loading of the 
program. First, all programs written for 
public distribution should leave undisturbed 
locations 000-010 of RAM memory page 
for the user's own system restarts. Secondly, 
Galaxy appears to have been written for use 
on a standard, full width Teletype. Many 
hobby systems, however, make use of a 32 
column television display. Fortunately, the 
source code documentation is sufficient for 
most programmers to reformat the output to 
fit their own system. It also would have 
helped if ASCII text messages had been 
actually listed alongside the octal dumps in 
the object code. 

So, if you've always wanted to command 
your own starship and if you have an 
8008/8080 system with at least 4 K 
memory, then Scelbi's Galaxy Game for the 
8008/8080 is a worthwhile addition to your 

Software library." William E Severance Jr 

Center Lovell ME 04016 



74 



ALTAIR OWNERS!... WANT TO COM- 
MUNICATE WITH THE ANALOG 
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Set. Tim. 5 Micro-Sec N/A 

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Ext. In. N/A Start*, Analog in 

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Offering the complete line 
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The Computer Store Inc. 

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♦Altair is a registered tradename of 
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75 




Here lies documenta- 
tion of known bugs de- 
tected in previous editions 
of BYTE. .. 



Author Roger L Smith sends in the 
following update on his article which 
appeared in the May BYTE: 

(a) Two minor errors appear in the 
schematic for the PROM programmer 
(see page 31, May 1976 BYTE). Those 
elusive little dots showing connections 
should show the junction of the 10 k 
and 27 k resistors connected to +80 V 
(near the 5 ohm resistor on MJE1102 
collector). 

(b) The second connection should 
show the cathode of the 1N270 and 
the 200 pF capacitor connected to the 
line to pin 15 of the PROM. 

If anyone is having trouble finding 
the 1N270 diodes (germanium), I have 
an alternate circuit that does not use 
these diodes. I'll send a copy of the 
schematic to anyone sending a SASE. 

[Roger L Smith, 4502 E Nancy Ln, 
Phoenix AZ 85040.] 

The following figures illustrate the fixes (a) 
and (b) to the diagram as originally 
published: 



02(4) 



ADD DOT HERE 




(a) 




ADD DOT HERE ■ 



(b) 



Author Phillip L Hansford reports the 
following glitch in the commentary of the 
MATCH program listing, page 49, June 1976 
BYTE: The instruction at 002/007 points 
the DE register pair to the output, not HL. 
All the other information on that line is 
correct." 



Argyle W Bridgett, an independent com- 
munications engineering consultant (39 
Chaske Av, Auburndale MA 02166) reports 
the following error in Don Lancaster's 
"Build the BIT BOFFER," page 30 in the 
March 1976 BYTE. The circuit originally 
published as part of figure 6 as a zero 
crossing detector would not be a good zero 
crossing detector according to Mr Bridgett, 
since it would tend to provide an oscillatory 
race condition. However, checking the print- 
ed circuit layout, Mr Bridgett found that 
the correct non oscillatory connections had 
been implemented. He states that the cor- 
rect connections for IC4C and IC4D are as 
follows: 




The dotted lines indicate connections to 
the remainder of figure 6's diagram. Several 
other individuals have mentioned this error 
as well." 



In a label of the cabling diagram for the 
serial chassis connector, figure 4, page 46, 
June 1976 BYTE, the phrase "110 BAND" 
should read "110 BAUD"." 



JITTER 

Bob Van Valzah, 1140 Hickory Trail, 
Downers Grove IL, reports a problem on 
page 94 of the June BYTE, in the RND 
routine shown. The proper code for the 
DCR C instruction at 000/136 is octal 015. 
Bob Baker, 15 Windsor Blvd, Atco NJ 
08004, suggests that Gordon Speer's RND 
routine will not really provide pseudo ran- 
dom numbers as it stands. The results of the 
exclusive OR and rotate bit manipulations 
are lost unless the accumulator is saved in 
memory. Bob suggests inserting MOV M,A 
between the instructions shown at locations 
000/113 and 000/114. Reassembly is not 
required if the program is just shifted down 
one byte to make room for the octal 167 
code required." 



76 



Classified Ads for Individuals and Clubs 



WANTED: I am looking for a used or nonfunction- 
al minicomputer, Altair, IMSAI, home brew, etc. I 
also need parts, boards, keyboard, tape drive or ? 
(you name it). Price is open. Write Steve Kelley, 
9506 Peach St, Oakland CA 94603. 

TRADE OR SELL: One Processor Technology 
Company 2 K EROM board with 16 1702As (total 
4 K) for $150 or best offer. MM5320 video timing 
chip, $15. XR-210s $3.50, Intel 8214 PICU, $17. 
WANTED: Paper tape reader. Need information on 
acoustic coupler sold by SSM. Glenn Nelson, Box 
1846, Brown University, Providence Rl 02912, 
(401 (274-5794. 

WANTED: Back issue of BYTE: I want to com- 
plete my collection. If you have a BYTE #4 you 
can do without, send your asking price to me: 
Keith Petersen, 1418 Genessee Av, Royal Oak Ml 
48073, (313)588-0184. 

FOR SALE: (2) Altair 8800s, with 1 K of memo- 
ry. Processor Technology full width mother 
boards, and custom card cages. Processor Technolo- 
gy: 4 K RAM board, 3P+S IO module, VDM-1 
display module, SWPT TVT-II with extras, God- 
bout 4 K RAM board, plus more. Eric Bjornsen, 
WB9HBP, 1615 East St, Baraboo Wl 53913. 
Phone: (608)356-5309. 

FOR SALE: Surplus, but new, never used HIT 
(Hobbyist Interchange Tape) system cassette inter- 
face unit. Allows user to store digital data on a 
cassette recorder. Assembled unit with information 
manual, $10.95. Matthew Smith, POB 373, Engle- 
wood CO 801 10. 

WANTED: Manual, schematic, and service data for 
Burroughs Model 9350-2 communications ter- 
minal-printer. M D Cassetti, 1011 Devonport Ln, 
Seabrook TX 77586. 

FOR SALE: SWTPC CT-1024 TV terminal with 
chassis, power supplies, and parallel interface 
board. Completely operational; all for $150. 
Richard Coates, 4610 Allan Rd, Milwaukie OR 
97222. 



FOR SALE: Several items in the following cate- 
gories: 35 Tee Dee, stand alone and ASR, 35 
reperf, 35 page printer and keyboard, 35 reperf's, 
32 and 33 keyboards, other 5 and 8 level TTY 
gear, SASE for listing and prices. CC Armstrong, 
3109 E Roma Av, Phoenix AZ 85016. 

FOR SALE or SWAP: Prentice Electronics type 
P-LLA leased line adapter (modem) at 600 baud 
max. Three plug-in units with rack mount en- 
closure and plug-in power supply: list price $800, 
asking $225 or swap for audio equipment. R 
Omegna; 130 New Rd Apt F9; Parsippany NJ 
07054. 

Bidirectional tape deck, model KP345 Pioneer. 
Brand new, factory warranty. Playback only, but 
may be modified by user to record. Direction 
controlled electrically. Only $60 plus UPS. Write 
Dale Freye, PO Box 703, Muskegon Ml 49443. 

FOR SALE: Altair 8800 power supply, trans- 
formers and extra 5 V/4 A output, $60; SWTP TV 
Typewriter II with PS, cursor control and serial IO 
in chassis with extra 5 V supply, switches and 
connectors, $225; SWTP parallel IO and screen 
read, $30 for both; Motorola video monitor and 
ASCII keyboard in molded cases, $110; Telex 
Termicorder cassette with digital R/W and PS 
electronics, $85; Model 33 KSR TTY with manu- 
als, pedestal, copyholder, dust cover, paper and 
ribbons $660. M J Hnetynka, 2043 Farmsville Dr, 
San Antonio TX 78245. 

8008 Users: I have written an 8008 self assembler, 
which is available to you. Send 25£ for a flier 
describing this assembler to Robert Heller, PO Box 
281, Wendell MA 01379. 

Before sending your classified 
ad to BYTE, read it over. Did 
you include your name, ad- 
dress, phone number (with 
area code) in the text of the 
ad? B YTE has received several 
ads with incomplete phone 
numbers or missing addresses. 



Readers who have equip- 
ment, software or other items 
to buy, sell or swap should 
send in a clearly typed notice 
to that effect. To be consider- 
ed for publication, an adver- 
tisement should be clearly 
non-commercial, typed double 
spaced on plain white paper, 
and include complete name 
and address information. 
These notices are free of 
charge and will be printed one 
time only on a space available 
basis. Insertions should be lim- 
ited to 100 words or less. 
Notices can be accepted from 
individuals or bona fide com- 
puter users clubs only. We can 
engage in no correspondence 
on these and your confirma- 
tion of placement is appear- 
ance in an issue of BYTE.* 



The Data Domain is a computer store serving the Central U.S. Many of you have already 
contributed to our success, and we wish to thank you. If you have not yet entered The Data Domain, 
we'd like to hear from you. We are here to serve your needs with a full line of products and services, 
and to offer assistance in solving both hardware and software problems. 

The retail computer store is more than a business to us. The Data Domain is a personal commitment 
of over 18 years of computer experience toward the growth of this new facet of our industry, which we 
are convinced will be of major significance to our nation's future in science, education and business. 




ATA 



O 



OMA/N 



111 S. College Ave. 

Bloomington, Indiana 47401 

Phone (812) 334-3607 

Offering IMSAI Processors and all major brands of accessories 



77 



What's 

New? 



Photo J: The HP-91 
shown in a working setting 
which emphasizes its 
portability. 




Calculator of the Month Club? 

Sometimes, one gets the impression that 
all the manufacturers of programmable (and 
non programmable) calculators have gotten 
together and agreed to have a calculator a 
month hit the market. The latest item to 
pass BYTE's desk in this area is the new 




Photo 2: The HP-91 anatomy following dissassembly of its case and removal 
of the processor /printer /battery subassembly from its mountings. 



HP-91 portable scientific printing calculator. 
As a portable calculator, this item looks like 
a first in the field with its printing capability 
and power supply. It is not a programmable 
calculator, however, being based upon the 
widely used HP-45 scientific calculator. Its 
primary added feature is the small alpha- 
numeric printer which has several modes of 
operation ranging from a complete printed 
log of operations to an on demand printing 
of register contents. 

Photo 1 is the beauty contest photo 
showing how the HP-91 fits into a typical 
briefcase of the businessman, engineer, stat- 
istician or scientist (any of whom would 
find its $500 price quite attractive con- 
sidering the printing functions). Photo 2 is 
the one which BYTE readers will find most 
interesting: the anatomy of an HP-91. No 
detailed analysis of this picture was supplied 
with the press release, but from the photo- 
graphic evidence some future technological 
archeologist might conclude that it was 
composed of a keyboard scanning subas- 
sembly, proccssor/printer/battery subas- 
sembly, case and AC power supply module. 

ROM programming for the HP-91 is a 
more powerful version of the HP-45 pocket 
calculator, with the added capability of 
creating a printed log of all calculations. It 
has all of the functions of the HP-45, plus 
expanded memory and additional functions 
like linear regressions. 

The HP-91 's new, built in printer can be 
operated in a "manual" mode which prints 
only when "Print x" or a list function is 
pressed, "normal" mode which prints all 
entries and functions, or the "all" mode 
which prints digit entries, functions, and 
results. It will print a display in fixed 
decimal, scientific notation and engineering 
notation (values with exponents that are 
multiples of three). 

A 220 page owner's handbook is included 
with the calculator. It contains user instruc- 
tions and a comprehensive application sec- 
tion that gives the most efficient keystroke 
sequences for solving problems in the fields 
of mathematics, statistics, finance, naviga- 
tion and surveying. An AC adapter/recharger 
and a carrying case also come with the new 
calculator. 

The HP-91 scientific printing calculator is 
manufactured and marketed by Hewlett- 
Packard's Advanced Products Division, 1501 
Page Mill Rd, Palo Alto CA 94304. 

Will the calculator a month trend con- 
tinue? Read the next BYTE and find out. 
Maybe HP will take the HP-55, put it into a 
case with a printer and batteries, and call the 
result a portable desk top programmable 
machine." 



78 



PHILADELPHIA 
COMPUTER STORE 

features 

The Personal 

Computer System 

IMSAI ® 
the digital group 



P 



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Computer 

Corporation 



phone: 

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A 103 



79 



You'll Want to Nybble at these 
Byte Books 




• The TTL Cookbook by Don Lancaster, published by 
Howard W Sams, Indianapolis, Indiana. Start your quest for data 
here with Don's tutorial explanations of what makes a TTL logic 
design tick. 335 pages, $8.95. 

• The TTL Data Book for Design Engineers, by Texas 
Instruments Incorporated. How does an engineer find out about 
the TTL circuits? He reads the manufacturer's literature. This 
640 page beauty covers the detailed specs of most of the 7400 
series TTL logic devices. No experimenter working with TTL has 
a complete library without The TTL Data Book for Design 
Engineers. Order yours today, only $3.95. 

• The Supplement to The TTL Data Book for Design 
Engineers, by Texas Instruments Incorporated. What happens 
when you can't find a 7400 series device listed in The Data Book 
for Design Engineers? Before you start screaming and tearing 
your hair out in frustration, turn to the Supplement. The 
Supplement has 400 pages of additional information including a 
comprehensive index to both TTL Data Book volumes. To be 
complete (and keep your hair in place and vocal cords intact) 
you'd best order the supplement at $1.95 to accompany the 
main volume. 

• The Linear and Interface Circuits Data Book for Design 
Engineers, by Texas Instruments Incorporated. When you run 
across one of those weird numbers like 75365 the immediate 
frustration problem occurs again. What kind of gate could that 
be? We won't tell in this ad, but you can find out by reading the 
specifications in The Linear and Interface Circuits Data Book for 
Design Engineers. You can interface your brain to the 72xxx 
(linear) and 75xxx (interface) series of functions by ordering 
your copy of this 688 page manual at only $3.95. 

• The Semiconductor Memory Data Book for Design 
Engineers, by Texas Instruments Incorporated. Don't forget the 
importance of memories to your systems. Refer to this 272 page 
manual to find out about the Tl versions of many of the popular 
random access memories and read only memories. Order your 
personal copy today, only $2.95. 



Where does the editor of a computer magazine turn 
when he must verify some author's hardware design? 
Information on a 75450 interface gate, or a 74147 
priority encoder circuit does not spring forth by magic. 
Checking the information supplied by authors is part of 
BYTE's quality control program. 

When you build a project, you need this same sort of 
information. All you find in the advertisements for parts 
are mysterious numbers identifying the little beasties . . . 
hardly the sort of information which can be used to 
design a custom logic circuit. You can find out about 
many of the numbers by using the information found in 
these books. No laboratory bench is complete without 
an accompanying library shelf filled with references - 
and this set of Texas Instruments engineering manuals 
plus Don Lancaster's TTL Cookbook will provide an 
excellent starting point or addition to your personal 
library. 

• The Transistor and Diode Data Book for Design Engi- 
neers, by Texas Instruments Incorporated. You'd expect a big 
fat data book and a wide line of diodes and transistors from a 
company which has been around from the start of semicon- 
ductors. Well, it's available in the form of this 1248 page manual 
from Tl which describes the characteristics of over 800 types of 
transistors and over 500 types of silicon diodes. This book covers 
the Tl line of low power semiconductors (1 Watt or less). You 
won't find every type of transistor or diode in existence here, 
but you'll find most of the numbers used in switching and 
amplifying circuits. Order your copy today, only $4.95. 

• The Power Semiconductor Handbook for Design Engi- 
neers by Texas Instruments Incorporated. To complement 
the low power transistor handbook, Tl supplies this 800 page 
tome on high power transistors and related switching devices. 
Here is where you find data on the brute force monsters which 
are used to control many Watts electronically. Fill out your 
library with this book, available for only $3.95. 

• Understanding Solid State Electronics by Texas Intru- 
ments Incorporated. This is an excellent tutorial introduc- 
tion to the subject of transistor and diode circuitry. The book 
was created for the reader who wants or needs to understand 
electronics, but can't devote years to the study. This 242 page 
softbound book is a must addition to the beginner's library at 
only $2.95. 

• The Optoelectronics Data Book for Design Engineers by 
Texas Instruments Incorporated. This 366 page book is a 
compendium of information on Tl phototransistors, LEDs and 
related devices. Order yours at $2.95. 



_TTL Cookbook @ $8.95 
_TTL Data Book @> $3.95 



.Supplement to TTL Data Book <s> $1 .95 
.Linear and Interface Circuits @ $3.95 
.Semiconductor Memory Data <s> $2.95 
.Transistor and Diode Data Book @ $4.95 
.Power Semiconductor Handbook <s> $3.95 
.Understanding Solid State Electronics @ $2.95 
.Optoelectronics Data Book @ $2.95 



Please add 75 cents for postage and handling. 

Send to: Name 



Please allow six weeks for delivery. 



Address 



City 



State 



Zip 



EITt 



Check enclosed 

Bill MC # 

Bill BA# 



.Exp. Date. 
.Exp. Date. 



PETERBOROUGH, ISIH 03458 



Signature 



80 



Software Bug 
of the Month 3 



Backus Normal Form, or Backus-Naur 
Form, or BNF, is often used to define the 
syntax of a programming language. Suppose 
we want to define a GO TO statement. We 
can write 



<GO TO statement) ; 



'GO TO' (label) 



(read "A GO TO statement is defined as the 
words GO TO followed by a label"). 

If you are writing a compiler, and the 
compiler reads a statement in the program it 
is compiling, it can find out whether that 
statement is a GO TO statement by looking 
first for the words GO TO, and then looking 
for a label. The order in which this is done is 
directly related to the BNF definition above. 
This suggests the following general pro- 
cedure: Suppose we have a BNF rule of the 
form 

<A> :: = <B> I <C> <D> 

(for example), or "An A is either a B, or else 
a C followed by a D." Now suppose we want 
to write a program to read a string and tell 
whether it is an A. Such a program is called a 
recognizer, and we can write it as follows. 
Suppose that we already have recognizers for 
B, C, and D (we are going to write the 
simpler recognizers first). Then our recog- 
nizer for A calls the recognizer for B. If it 
finds B, it stops. If it doesn't find B, it goes 
back and calls the recognizers for C and D. 
The recognizer for C leaves its pointer to the 
string at the beginning of what is presumably 
a string which is a D. 

A programmer tried this out on the 
standard BNF definition of an unsigned 
integer: 
(unsigned integer) :: = (digit) ||(unsigned integer) (digit) 

and ran into no end of difficulties. First his 
program gave the wrong answer; he found 
the problem, fixed it, and got an endless 
loop. He thought he found that problem, too, 
and fixed it again, but he still got an endless 
loop, in a different place. See if you can 
reconstruct his plight. 



Answer in Next Month's BYTE 



SOLUTION TO BUG OF THE MONTH #2 

Never mind that the program is written in 
a very awkward way, and that you can 
probably find lots of ways to write it better. 
The puzzle last month was to find the bug in 
the program as it stood. If you didn't do 
that, you haven't solved the problem. 

Ready for the solution? 

This bug may or may not occur, de- 
pending on the computer system you're 
using. The trouble is that it looks like a bug 
in iteration, when in fact it isn't that at all: 
It's a bug in floating point arithmetic. The 
quantity DEGREE is one degree in radians, 
approximately. One degree in radians 
doesn't come out even as a binary fraction, 
which is the way real numbers are repre- 
sented in computers. The result is that, when 
you add this number to itself, as we did in 
this program, the answer is still an approxi- 
mate number. When you get up to 
PI/2+DEGREE, which amounts to 91°,- 
the answer apparently was just a hair too 
small. If X had been equal to PI/ 
2+DEGREE, it would not have been less 
than this, and we could not have done the 
91st case. But as it is, the 91st case was 
done." 



W Douglas Maurer 
University Library Room 634 
George Washington University 
Washington DC 20052 



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81 



Still More 

BYTE's 

Books 





•DESIGNING WITH TTL INTE- 
GRATED CIRCUITS by the Components 
Group, Texas Instruments Inc. Edited by 
Robert L Morris and John R Miller. 

People often ask questions like "Where 
do I get basic information on hardware 
design?" One answer is in "Designing With 
TTL Integrated Circuits." 

This book, published by McGraw Hill in 
1971, is a fundamental starting point for 
any person designing peripherals and custom 
logic employing TTL integrated circuits. 
While its publication date precludes any 
reference to the later additions to the TTL 
7400 series of components found in the 
Data Books, it is nevertheless the source of a 
wealth of ideas on TTL integrated circuits 
and design of logic with this family of 
circuits. 

What is fanout? You may have heard this 
term mentioned at computer club meetings 
or in advertisements for circuitry, or in 
articles in BYTE. You can find out 
background information on the calculation 
of fanouts by reading the chapter on Circuit 
Analysis and Characteristics of Series 54/74. 

Worried about noise, shielding, ground- 
ing, decoupling, cross talk and transmission 
line effect? (Or, more properly, did you 
know you should worry about these effects 
in certain circumstances?) Find out about 
general precautions and background infor- 
mation by reading the chapter on Noise 
Considerations. 

The chapter on Combinatorial Logic 



Design gives 53 pages of background 
information on Boolean algebra and practi- 
cal representations of logic in the form of 
SSI gates. The chapter includes a description 
of Karnaugh mapping techniques and the 
minimization of logic. From combinatorial 
design, the book progresses into Flip Flops, 
including background information on the 
workings of these devices, and fairly 
detailed descriptions of the uses and 
applications of these devices including 
synchronization of asynchronous signals, 
shift registers, flip flop one shots, etc. Then 
the book returns to static combinatorial 
logic with its description of the Decoders 
available in the 7400 line as it stood in 
1970-1971. 

A chapter on Arithmetic Elements gives 
fundamental descriptions of binary arithme- 
tic, diagrams of the basic gate configurations 
for combinatorial logic adders, and a section 
on number representations for use in 
computers. Much of the material in this 
section is dated, due to the fact that the 
later 74181 series of multiple function 
arithmetic units had not yet appeared when 
the book was written. But for a background 
on arithmetic operations implemented with 
the simpler 7483 circuits, this chapter is 
ideal. A chapter on Counters and a chapter 
on Shift Registers complete the detail logic 
sections. The book is closed out by a 
chapter on miscellaneous Other Applica- 
tions including a simple binary multipliers 
12 hour digital clock and a modulo-360 
adder. 



BIT! 



PETERBOROUGH, NH 03458 



"1 



Designing With TTL Integrated Circuits $24 

Microcomputer Design $25 

Send to: Name 



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Please allow six weeks for delivery. 



The most important use of this book is its 
value as an introduction to TTL logic. By 
reading and studying it, you will begin to 
understand the ways in which SSI and MSI 
TTL gates can be utilized in your own 
experimental logic designs. After studying 
this text, you should be able to make much 
more sense out of the technical information 
summaries typically published as specifica- 
tions sheets and data catalogs. 

Order your copy today from BYTE's 
Books, $24 postpaid. 

•MICROCOMPUTER DESIGN by Don- 
ald P Martin, Martin Research. Edited and 
Published by Kerry S Berland, Martin 
Research. 

Purchase your copy of the definitive 
source for circuitry and hardware design 
information on the 8008 and 8080 com- 
puters today. 

Even Intel, the originator of the micro- 
processor revolution, is hard put to compete 
with the wealth of information found in 
Martin Research's new second edition of 
Microcomputer Design. This is the book 
which was originally published as an 
expensive (but quite practical) engineering 
report in loose leaf form, at about the time 
the microprocessor technology was first 
catching on in the form of the 8008. This 
388 page second edition of the manual is 
loaded with detailed information on how to 
build and use computers based on the 8008 
and 8080. 

But even if you do not intend to use the 
8008 or 8080, the practical pointers on 
digital logic design, peripherals and applica- 
tions of hardware techniques will more than 
justify the new low price of $25 for this 
handbook. Microcomputer Design is a must 
for 8008 owners and 8080 owners who 
want to truly understand how their 
processors process. 

Microcomputer Design is complete with 
numerous illustrations, tables and diagrams, 
plus reprints of the specifications sheets for 
the Intel processors. There are numerous 
practical examples of circuitry and many 
complete computer designs ranging from 
"minimal microcomputers" to a full blown 
8080 processor. 

Order your copy today, $25 postpaid 
from BYTE's Books. 



82 



What's New? 




Sphere Graduates and Goes 
to Work for Businesses 

Sphere Corporation, 940 North, 400 
East, North Salt Lake UT 84054, has just 
announced a new series of products designed 
for the small business environment. The 
Sphere Series 500 is a desk top computer 
based on the Motorola 6800 processor, 
complete with a video display of 80 charac- 
ter per line, upper and lower case. The 
system comes with executive programs in 
read only memory. A version of BASIC is 
provided with the hardware. In its minimum 
form, the Model 520 is described as a 4 K 
byte serial interface intelligent terminal. 
Data can be selected from cassette tape or 
modem, RS-232 communications line, Tele- 
type, or direct TTL interfacing at rates up to 
9600 Baud. A resident 4 K BASIC option 
gives this programmable unit independent 
intelligence. 

Next in the line is the Model 530, which 
features 20 K bytes of memory and a dual 
cassette operating system with extended 
BASIC. This version is intended as a means 
for the small business to do tape oriented 
batch processing of data. The Model 540 is 
billed as a 20 K byte system with a floppy 
disk operating system, extended BASIC and 
a 110 line per minute 80 character wide 
printer. The floppy disk operating system 
speeds up systems functions by a factor of 
about 20 relative to the cassette tape ver- 
sion, and provides the ability to have signifi- 
cant on line random access files within the 
capacity of a floppy disk. Finally, at the top 
end of the line is the Model 550, which is a 
540 with 54 K of memory on line and a 1 32 
character wide printer. 

These units are intended for business 
applications and are sold completely 
assembled. For detailed information contact 
Sphere Corporation at the address above." 



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83 



What's an l 2 L (I squared L)? 



Terry Steeden 
40 Waseca Av 
Tonka Bay MN 55331 



Figure I: Logic Gates. The 
conceptual schematic of a 
typical TTL logic gate, 
with its logic diagram, is 
shown in (a). The equi- 
valent logic function as an 
fiL gate is shown in (b). 
Note that the TTL gate 
utilizes several resistors as 
part of its structure, 
whereas the fiL gate uses 
transistors exclusively. 
This results in a much low- 
er power dissipation for 
the chip since there is no 
IR2 resistive loss involved 
in the l?L gate. 




■OVCC 




o 



Everyone likes transistor-transistor logic, 
TTL. It is fast, cheap, widely available — and 
it consumes power. Not much power, com- 
pared to a vacuum tube, but a lot for 
integrated circuits, especially when com- 
pared to metal oxide semiconductors. And 
everyone likes MOS because of its low power 
consumption. But, it is typically not as fast 
as, and it is not as cheap as, the older TTL 
logic. This means that Large Scale Integra- 
tion (LSI) chips either draw a lot of power 
(TTL) or are not as fast as they could be 
(MOS). But what would happen if the best 
of the two could be joined together? A fast, 
low power, cheap gate . . . Behold, |2l or 
"integrated injection logic." Let's see how 
low power and speed are combined cheaply. 
We can begin by looking at power consump- 
tion, cost, and speed, briefly, and then see 
what other observations we can make about 
|2L. 

Conventional TTL Gates 

What is it that draws power in the 
conventional TTL logic gate? Mainly, the 
necessity of resistors. Power consumed will 
obviously be reduced if these resistors can be 
removed. Figure 1a is a conceptual schemat- 
ic of a conventional TTL logic gate, and 
figure 1 b is an |2l logic gate. Note that both 
perform the same function and |2l does it 
with no resistors. The transistors have been 
merged (|2l is also called merged transistor 
logic). This lack of resistors results in a 
tremendous power savings. (Also note that 
the |2l gate has an extra pin marked Vjj — 
we will refer back to this when talking about 
speed.) 

Cost is the second factor to consider. 
Figure 2a is a possible configuration using a 



84 



A 

vcc 



n 



U N U 



C B E 



W 



5 

VCC 



n 



1 P J N P 


P 1 N+ J P 




•— 


A 


N + 





Figure 2: Junction Fabri- 
cation Economies. The 
/2L gate could be 
fabricated using a chip lay- 
out similar to TTL as is 
shown in (a). However, the 
physics of the I^L design 
allows the manufacturer to 
merge the two transistors 
as shown in (b), a trick 
which simplifies the pro- 
cessing of the silicon and 
reduces the cost of fiL 
gates. 



conventional layout of |2l, with a laterial 
PNP and diffused isolation (note the 
jumper). All together, seven masks must be 
used by the manufacturer to produce the 
circuit, which in this configuration is similar 
to TTL. Figure 2b is the same circuit with 
the transistors merged. The base of the PNP 
has been placed at ground and the NPN 
inverted (collector and emitter roles re- 
versed). No jumper is required because the 
two P junctions are now on one strata. Most 
important, only four masks are required for 
manufacturing. We now have three reasons 
for cost reduction. One, less complicated 
masks and less processing because of 
merging. Two, existing TTL and CMOS 
technology and manufacturing processes can 
be used to produce the |2l circuits, thus 
keeping research and development costs 
minimal. Three, merging saves space allowing 
more gates per unit area, keeping cost per 
circuit down. 

Now, about that pin marked Vjj, and 
what about speed? Pin Vjj is a new power 
pin. This means |2l has two power pins, V cc 
and Vjj. V cc is the conventional 5 Vdc, and 
Vjj is the voltage input which determines the 
speed of the chip (see figure 3). Observe that 
the less power presented to a theoretical |2l 
gate, the lower the obtainable speed of the 
gate. Take note also how |2l compares with 
CMOS and LS gates. Basically, more speed 
can be obtained at the expense of more 
power, all controlled at pin Vjj. This speed is 
adjusted by picking a resistor to limit power 
to Vjj. In general, the voltage to be limited is 
known (usually 5 Vdc) and the current to be 
supplied Vjj is picked depending on the 
speed required. Knowing voltage and cur- 
rent, ohms law will supply a ballpark value 



for the resistor. It is possible that in the 
future this external resistor may be made 
internal to the package. Hopefully, at this 
point, the reader can see the obvious relation 
between speed and power. The power is 
always less than CMOS or TTL operated at 
the same frequency. By slowing down the 
speed of the |2l gates, even more power can 
be conserved. 

Now what other observations and data 
can be added to our basic knowledge of |2l? 
According to Signetics, a major producer 
and developer of |2l, |2l will be manu- 
factured for the next couple of years to be 
compatible with TTL logic levels. TTL logic 
levels are conventionally determined to be 
to 0.8 Vdc (logic 0) and 2.4 to 5 Vdc (logic 
1), a voltage difference of as much as 5 V. 
|2l logic will use only a 0.6 Vdc difference 
between logic and logic 1 . This means that 
for |2l to be compatible with TTL, input 
and output interface logic must be added to 
shift the l 2 L levels to TTL levels. After a 
couple of years this interface logic will be 
dropped and pure |2l systems will be 
available. 

Signetics would also make us aware that 
|2l is not to replace TTL or CMOS, but has 
been introduced to fill the void that now 
exists in the 2 to 20 MHz operating region. 
Higher voltage |2|_ is also being produced to 
be compatible with CMOS. Thicker masks 
will handle the higher voltage, 15 Vdc, but 
slows the gate time. 30 V logic is not likely 
at this time because of the extreme slowing 
due to the thicker layers. 

REAL Practical Terms 

Finally, then, what does all this mean in 
real practical terms for us the users? Let's 



85 



POWER/GATE 
IOMW 



100/iW 



IG>W 



l(jW 





LS 














5V CMOS 








/l 2 L 













lOKHz lOOKHz 



look at Signetics |2l Deskew FIFO chip as a 
real practical example. We will notice first of 
all that a single gate size is 1.5 mi|2 (968 
mm2). The pads for wire attachments are 
huge by comparison, 16 mi|2 (10,322 mm2). 
[1 mil = 1 inch/1000]. Smaller gate size 
means more logic per unit area. (This is to 
imply that |2|_ is most practical for LSI and 
not for small or medium scale integration, 
SSI or MSI). The entire Deskew chip 
measures 125 mi|2 (0.081 mm2). The |2l 



Figure 3: Speed Versus 
Power. This graph indi- 
cates the typical rela- 
tionship of power require- 
ments versus operating 
frequency for three 
families of logic. The LS 
designation stands for low 
power Shottky TTL gates. 
The 5 V CMOS curve is 
typical of CMOS gates run 
at a Vcc of 5 V. The &L 
curve dips under the other 
two in all cases, thus indi- 
cating superior efficiency. 



portion of the chip measures 90 mi|2 (0.058 
mm2). The remainder of the chip is TTL 
interface circuitry. The |2l portion of the 
chip, 90 mi|2, draws 200 mW at 10 MHz. 
The TTL interface circuitry, a much smaller 
35 mi|2, draws 220 mW at the same speed. It 
can be seen that the chip saves considerable 
power when compared to TTL Deskew 
chips. And once the TTL interface circuits 
are dropped so pure |2l logic is used, even 
more power will be saved. Complete systems 
using several amps of power in TTL will 
require only milliamps in |2l. 

Basically then, what can be said of the 
|2l logic? It is a high density logic, which 
can be made with existing technology and 
processing. It draws little power and pro- 
duces high speed. It can be speed adjusted to 
match TTL, 10 device, or RAM, ROM, or 
PROM speeds. And at this point in time, all 
matching TTL interfaces are typically con- 
tained on the |2l chip. One last thing: |2l 
outputs are always open collectors useful for 
"wired OR" or data bus circuitry. The new 
|2l logic is an exciting and most advanced 
technology that will be more and more a 
significant addition to the field of elec- 
tronics." 



What's 

New? 



The I MSA I 8080 

The IMSAI 8080 is a microcomputer 
designed for a wide variety of applications, 
including commercial OEM, laboratory 
prototype, as well as a central processor for 
small stand alone systems. Contrary to some 
popular misconceptions, the IMSAI 8080 is 
not a Japanese import computer, but is a 
product of IMS Associates Inc, 1922 Re- 
public Av, San Leandro CA 94577. It is 
ruggedly constructed around an anodized 
aluminum card cage and printed circuit 
Mother Board which accommodates the 
front panel and up to 22 plug in cards for 




memory and IO interface devices. The heavy 
duty lucite front panel has an extra 8 
program controlled LEDs as well as rugged 
commercial grade paddle switches backed up 
by reliable debouncing circuits. The IMSAI 
8080 power supply has a steady state 20 
Amp current capacity, enough to power a 
full system. 

The 8080 can be expanded to a powerful 
system with 64 K bytes of memory plus a 
floppy disk controller with its own on board 
8080 microprocessor and a disk operating 
system. 

A wide variety of IO devices including an 
audio tape cassette interface, printer, video 
terminal and teletypewriter can be used with 
the 8080. These peripherals will function 
with an 8 level priority interrupt system. 
BASIC software is available in 4 K, 8 K and 
1 2 K, obtainable in PROM. 

The IMSAI 8080 can be ordered directly 
from the factory in either kit ($599) or 
assembled ($931) form. For dedicated OEMs 
that don't require a front panel, $729 
assembled, $529 unassembled. Both the kit 
and the assembled IMSAI 8080 come with 
documentation, including an Intel Data 
Book, IMSAI 460 page Introduction to 
Microcomputers and IMSAI 8080 User's 
Manual. ■ 



Literature Available 

OK Machine & Tool Corporation, 3455 
Conner St, Bronx NY 10475, distributes a 
complete line of wire wrapping tools and 
accessories. Write to them and ask for 
catalog 36D (March 1976) and price 
schedule List No. 76-37A to find out about 
the details of their line." 



Don't Let This One SC/MPer Away 

Courtesy Stanley Veit, proprietor of The 
Computer Mart of New York Inc, we bor- 
rowed one of these National Semiconductor 
prototyping kits so that Ed Crabtree could 
take this picture. Stanley is retailing this 
complete "evaluation kit" from National 
Semiconductor through his store to many of 
the experimenters in the New York area. At 
a price less than that of a good quality high 
fidelity ti'rn table, you can try out micro- 
computer technology using a 20 mA current 
loop Teletype interface. The kit includes a 
ROM monitor program to drive the Tele- 
type, 256 bytes of programmable memory, 
processor, clocking and related circuitry. It 
comes with a voluminous pile of documenta- 



tion weighing 13.4 times the weight of the 
bubble packed processor and circuit card — 
all neatly contained in a loose leaf binder. 
Power requirements are +5 V at 350 mA, 
and -12 V at 200 mA. You should be able 
to "get on the air" with a standard Model 33 
or Model 35 Teletype after about one 
weekend of study and assembly using this 
kit. For retail purchase of this item, contact 
Stanley Veit at The Computer Mart of New 
York Inc, 314 Fifth Av, New York NY 
10001." 




Get a 



mouthful to 



talk about, 



Subscribe to 



mm 



QUALITY 

USED TEST EQUIPMT 

TEKTRONIX 

Oscilloscopes 

Plug-ins 

Sig. gen.s 

Carts 
HEWLETT-PACKARD 

Meters 

Probes 

Carts 
For a complete list of 
available items, write: 



PTI 



r I I Div. 12 
P.O. Box 8699 
White Bear Lake, Mn 
55110 



N. Y.'s Newest Store for 
Micro and Mini Compu- 
ter Hardware and Soft- 
ware. 

We will be featuring a 
large selection of: I MSA I 
(kits and assembled) Pro- 
cessor Technology's full 
line. Also a selection of 
choice modules from 
Cromemco, Solid State 
Music and others. Plus: 
full line of TTL logic, 
discrete components, 
memory and MPU chips. 

Audio Design Electronics 

487 Broadway Suite 512 
New York NY 10013 



87 











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Photo 1: The Spider. Roger Amidon's Spider is depicted in this photograph taken by Sol Libes, president of the Amateur 
Conjputer Group of NJ, during an informal tour of people's computers May I 1976. Believe it or not, the Spider works and is 
used by Roger as an element of his radioteletype station. Roger can work on Spider in a comfortable prone position on the 
floor. 



Systems of Note 



by Carl Helmers 
Photos by Sol Libes 



Here Is a second example of BYTE's Systems of Note feature. The purpose 
of Systems of Note Is to document what kinds of systems are being developed 
and utilized by our readers, and how they are viewing the computer systems 
field as reflected in their choices of hardware and software components. As 
an example of another system, here are my impressions of Roger Amidon's 
rather advanced shop. 

Each reader whose system description is submitted and published for this 
feature will receive an honorarium of $25 as BYTE's contribution to help 
further the state of the art . . . CH 



Roger Amidon's Spider (and Altair) 



Roger Amidon, a member of the Amateur 
Computer Group of New Jersey, was one 
stop on a tour of personal computers which 
Sol Libes arranged for several of the people 
visiting the ACGNJ Trenton Computer 
Festival May 2. Several years ago, Roger 
began work on his first personal computer, a 
12 bit machine which he and all his ac- 
quaintances call "the Spider." Before micro- 
processors, the only way to make a com- 
puter was to do the entire design from 
scratch using DTL and TTL integrated cir- 
cuits. Combine that with an amateur's 
pinched pocketbook, and some innovative 
(professional technicians please don't 
shudder too much) assembly methods will 
be required. Roger's Spider is built using one 
perforated board vaguely visible in photo 1 
(below table level at the corner between two 
tables) and a lot of little printed circuits 
which mount one IC and bring the leads out 
to solder pads. The interconnections are 



88 



made permanently, using recycled intercon- 
nection wire soldered to these pads. A fair 
number of alligator clip interconnections are 
also a permanent part of the system for 
selecting options. 

When I viewed the Spider on May 1, it 
was in operation (as it had been for some 
time, unbelievably) serving as a control 
element of Roger's amateur radio radiotele- 
type station, K2SMN. Roger demonstrated 
its operation using the Model 15 Teletype 
barely visible at the right of the picture. The 
physical arrangement spilling off the table 
onto the floor is due to a cat. According to 
Roger, he found his cat one day playing on 
the table in the middle of the Spider. Upon 
being discovered (and startled) the cat left 
rather quickly, but unfortunately was 
tangled in the web. A good portion of the 
web was dragged off the table. Not daring to 
move it (for fear of making any damage 
worse), Roger tried the machine out and 
found no damage. The serendipity which 
resulted is that Roger found it quite con- 
venient to work on Spider while lying down 
on the nice soft rug. 

Would Roger build a computer again 
using the Spider method? Yes and no. His 
current system, an Altair home brewed from 
boards purchased from MITS, was largely 
built using printed circuit and wire wrap. 
But elements of spiderism are found 
throughout the peripherals, and a small 
spider web was quite evident. However, 
there are some rather obvious disadvantages 
to the method. It lacks portability, it is 
prone to noise and RF pickup (a big part of 
Roger's component count is ceramic bypass 
capacitors), it has a certain lack of esthetic 
charm when viewed by some people, and so 
on. But it works. 

His present main system, seen in photo 2, 
consists of the home brewed Altair with 
40 K of home brewed memory, a 9 track 
surplus tape drive, a tape operating system 
with fairly advanced file management soft- 
ware for the tape drive, a video terminal 
borrowed from his employer, a model 35 
Teletype borrowed from his employer, etc. 
He has an excellent assembler and text 
editor in operation, and the system is par- 
tially used for software development in 
connection with his employment." 




Photo 2: Roger's "real" computer in operation. This photo, also by Sol Libes, 
shows Roger Amidon (seated) at the Teletype terminal of his system, with his 
main CRT display above. Looking over his shoulder (left to right) are Gary 
Coleman (president of the Midwest Affiliation of Computer Clubs), Carl 
Helmers (BYTE) and Hal Chamber/in (of the Computer Hobbyist/ The actual 
computer and 9 track tape drive are hidden by the onlookers. Elements of the 
Spider can also be seen between Roger and the terminals. 



ALTAIR 8800 OWNERS* 



We recently received the following letter: 



APRIL 26, 1976 



GENTLEMEN* 



I JUST WANTED TO TELL YOU THAT I THINK YOUR CLOCK FIX-IT KIT 15 
REALLY GREAT! I WAS HAVING TROUoLE RUNNING BASIC AND AFTER 
INSTALLING YOUR KIT FOUR OF »Y HITS BOARDS THAT WEREN'T RUi.MNG 
CAKE BACK TO LIFE AND NOW ARE HELPING ME TO WRITE THIS LETTER 
ON THE COMPUTER. ENCLOSED IS ANOTHER ORDER FOR A CLOCK KIT. 
THIS IS FOR THE SECOND ALTAIR THAT I 'AM NOW I ;-.' THE PP.0Cc.SS 
OF BUILDING. 
AGAIN MANY THANKS FOR SUCH A FINE PRODUCT. 



SINCERELY 
LLOYL L. S 



How well does your Altair run? 

A Clock Fix Kit is only $15 postpaid. 



PARASITIC ENGINEERING 



PO BOX 6314 



ALBANY CA 94706 



What's 

New? 



Use This for the "Ship's Console" of Your ENTERPRISE 



\" w . 



ADS has introduced the Univue keyboard 
and instrumentation enclosure designed for 
low profile instrumentation and computer 
data entry console applications. Special de- 




sign features include a welded 0.062 inch 
(1.6 mm) steel body of two piece construc- 
tion for strength and an outside removable, 
flush mounted aluminum panel. The 23 x 8 
inch (58.4 x 20.3 cm) front panel is removed 
via six mounting screws to give access to the 
enclosure interior. Over 200 cubic inches 
(3277 cc) of interior space is available for 
housing support electronics. The Univue 
body is coated with light gray lacquer type 
primer/surfacer to allow virtually any type 
paint to be used for the final finish. Overall 
size is 24 by 12 by 3 inches (61.0 by 30.5 by 
7.6 cm). The Univue is shipped with 
aluminum panel, heavy duty nonskid rubber 
feet, hardware, and finishing tips. Shipping 
weight is 17 pounds, with delivery from 
stock. 1-24 price is $32.95 from Advanced 
Data Sciences, PO Drawer 1147, Marion OH 
43302." 




Burn 2708 EROMs with This Programmer 

Intel Corporation's version of a micro- 
processor evaluation product is called the 
System Design Kit (SDK) and is based on 



the 8080 processor. But according to a press 
release from Microcomputer Techniques Inc, 
1120 Reston International Center, Reston 
VA 22091, there is no facility to program 
2708 EROMs with the SDK system. 

As a result, Microcomputer Techniques 
and Cramer Electronics have teamed up to 
supply a EROM programming board called 
the 2708 EROM Programmer Cramerkit 
which at a price of $129.95 adds the 2708 
programming capability to Intel's product. 
An 11 page application note on interfacing 
this programmer to the Intel SDK is avail- 
able, giving definitions of all the interface 
pins, board layout map, operating instruc- 
tions and a listing of the 8080 program 
which drives the interface in the context of 
the Intel SDK. Generalized software for the 
programmer is provided in the Cramerkit 
reference manual, which is available for $5. 
The software can easily be adapted to the 
Altair 8800 and other 8080 kits." 



Attention Retailers: Here is One Way 
to Sell Computers 

A relatively new retail computer opera- 
tion is the Personal Computer Corporation, 
located at Frazer Mall, Routes 30 and 352, 
Frazer PA 19355. The company has been in 
operation at the mall since March 9 1976, 
and features a full service computer store 
operation with the IMSAI and Digital Group 
products, a full time sales staff of three plus 
several part time people, and a full time 
programmer on the premises. The interesting 



retailing point is this: The company acts as a 
systems house by assembling a completely 
integrated system package called the "Per- 
sonal Computer System." The standard sizes 
are 6 K memory and 10 K memory, selling 
at $1495 and $1655, respectively — over the 
counter. These systems, according to the 
sales literature, come in an "attractive 
wooden cabinet with gold buffed and anod- 
ized covers and remote keyboard box with 
anti-glare top surface." The standard system 
includes video and tape interfaces with all 
hookup cables, power supply module with 



90 



NEW FROM MARTIN RESEARCH. . 



MODULAR MICROS . . . 

The modular micros from Martin 
Research provide all the advantages of 
microprocessor technology. These ver- 
satile printed circuit modules commu- 
nicate via a bus structure, compatible 
with: 

• The MIKE 3 series, based on the 
industry standard 8080 

. The MIKE 2, based on the 8008- 
for small industrial controllers 

• The new MIKE 8, based on the 
Z80 from Zilog/Mostek-combin- 
ing the best features of the 8080 
and 6800 




THE MIKE 3. . . 

The MIKE 3 typifies the modular 
micro approach. An optimal small 
system, yet fully expandable. The 
AT813 is a three-board system, based 
on the Model 471 CPU board, with an 
8080A microprocessor. The system 
comes with a Model 420 Console 
board, featuring a calculator-style key 
board and six fully-decoded LED di- 
gits. The third board is a Model 423 
PROM/RAM board, with 512 bytes 
P/4K) of RAM and a versatile MONI- 
TOR program in a PROM. The MONI- 
TOR allows the user to program the 
computer with the keyboard, visualiz- 
ing the results on the LED digits. (The 
423 board has capacity for up to 1K 
of RAM and 2K of PROM.) An ideal 
small system for prototyping and for 
educational use, the AT813 lists for 
only S395.00, fully assembled and 
tested. 

A similar MIKE 8 system, for the 
Z80, is available. Contact us for prices. 



NEW DEBUG SYSTEM! 

Martin Research takes pride in 
announcing the AT814, a MIKE 3 
computer featuring a powerful but 
low-cost diagnostic package. Designed 
for use in development, trouble-shoot- 
ing, and educational applications, the 
814 is one of the most powerful basic 
development systems available today. 

DEBUG PROM . . . 

This software package supple- 
ments the MIKE 3 MONITOR by al- 
lowing the user to step through pro- 
grams one instruction at a time, using 
the console keyboard. Unlike the step/ 
run switch on other computers, how- 
ever - which simply deactivates the 
CPU between instructions— the DE- 
BUG PROM maintains full processor 
activity. After executing each instruc- 
tion, the user can inspect the status of 
every data register in the computer— 
any desired memory location (includ- 
ing the program stack) and the 8080's 
internal registers and flags! Or, the 
user can set a breakpoint at any de- 
sired location, even a point in PROM 
or ROM memory. 




32-Channel Scope Display 

The 32-Channel Microprocessor 
Data Display allows the user to inspect 
all important computer signals on an 
external single-trace, triggered sweep 
oscilloscope, 16 channels at a time. 
When a switch on the Model 472 De- 
bug Board is pressed, the 16 address 
lines are displayed; otherwise, the data 
bus and selected control signals appear 
on the scope. Two probes on the 472 
board may be used to trace any de- 
sired signals in the computer. 



The AT814 comes with the 472 
Debug board (with space for custom 
interface circuitry), 471 CPU board 
(with 8080A), console board, and 423 
PROM/RAM board (MONITOR and 
DEBUG PROMs, and %K of RAM). 
Fully assembled and tested, the AT814 
lists for $495.00. 



microcor 



esign 




Thousands of copies of our in- 
novative book on microprocessors, 
published in 1974, were purchased by 
engineers and designers around the 
world. . . .for $75 each. Now, MICRO- 
COMPUTER DESIGN - revised, ex- 
panded, and reprinted in paperback 
-is available for $25.00! Over 400 
pages on quality white text paper, in- 
cluding: 

• 8080 circuits, theory o f opera t/on 

• Vectored interrupts, for all 8-bit 
central processing units 

• Efficient bus structure design 

• Interfacing to timers, A/D con- 
verters, keyboards, digits, and 
other I/O devices 

• Plus much more! 

SPECIAL: The MIKE 2 Manual 
is a complete guide to our 8008-based 
micro, with schematics, theory, and 
software listings for the MONITOR 8 
operating system. Over 1 50 pages long, 
the Manual normally costs $15. Now, 
MICROCOMPUTER DESIGN, plus 
this Manual, only $29.00! Applies to 
prepaid orders received before October 
1, 1976. 

BankAmericard, Master Charge accept- 
ed. U.S. prices-foreign delivery extra. 
Stocked by Semiconductor Specialists! 

3336 Commercial Avenue, Northbrook, 
I L 60062 USA • (312)498-5060 



modular micros 



martin research 



ample reserves for expansion, cooling fan, 
6 K of memory, operating system software 
on cassette tape and documentation. With 
expansion to 10 K using one 4K memory 
increment, the system comes with a 10 K 
BASIC package on cassette tape. Since the 
"Personal Computer System" package is sold 



as a complete unit over the counter, demon- 
strated at the store, the need to become a 
hardware hacker is minimized. Thus the 
number of potential customers is maximized 
and this product should sell quite well since 
it provides its buyer with a "minimum 
hassles" system. ■ 



Photo 1. 



Here's a Pair of Hardware Debugging 
Tools of Note 

Continental Specialties Corp has an- 
nounced two new debugging tools which will 
help you analyze hardware faults in circuitry 





Photo 2. 



of microcomputers. One is the $44.95 LP-1 
logic probe shown in photo 1. This is a hand 
held unit which uses system power supplies 
accessed via clip leads (with reverse polarity 
and over voltage protection). The input to 
the probe is high impedance (100 k ohms) so 
there is no loading problem in analyzing 
active digital circuitry. The input network 
includes a mode switch to select CMOS or 
TTL/DTL logic levels. 

The second product is billed as a "second 
generation logic monitor" and is the $125 
LM-2 instrument shown in photo 2. This is a 
16 pin parallel logic level indicator which 
clamps over the circuit under test, plus a 
separate power supply base with a logic 
family threshold selection including RTL, 
DTL, TTL, HTL and CMOS families. Since 
all power is derived from a separate power 
supply, there is no problem of overloading a 
system power supply during a test. Readout 
is at the top of the clip which interfaces to 
the integrated circuit under test." 



Attention: ALTAIR/IMSAI/MicroALTAIR Hardware Hackers 



A new universal microprocessor board, 
from Vector Electronic Company, lets 
Altair, IMSAI and other microcomputer 
users add circuits in a convenient and in- 
expensive manner. One universal board, 
identical in size to those used in the Altair, 
serves for RAM, ROM, or PROM memory 
expansion, for peripheral interface hardware 
requirements, or for IO circuits such as 
A-to-D, D-to-A converters, multiplexers and 
relays. 

The Vector model 8800 V board is pre- 
punched with 0.042 inch (1.1 mm) diameter 




holes on 0.1 inch (0.254 cm) centers so that 
the user can place dual in line packages or 
sockets in any location. Typically, the board 
holds two 40 pin DIPs, eight 24 pin DIPs 
and 36 14 or 16 pin DIPs. Alternatively, it 
can hold 52 14 or 16 pin DIPs, or ten 40 pin 
DIPs and eight 24 pin DIPs — or any 
combination in between. This flexibility is 
especially important with the 1 K or larger 
memory devices which may have 18, 20, 22, 
or 28 pin packages. 

The designer may use any dual in line 
packaged device without modifying the 
board. The boards also have space for 
discrete devices and for ribbon-wire con- 
nectors. Column and row zone coordinates 
as well as column and row hole designators 
are etched into the laminate. 

Power is distributed to each potential 
device location by the power and ground 
planes on opposite sides of the board. These 
also give distributed decoupling capacitance. 
Additional capacitors can be located 
adjacent to the DIPs. 

The board has two copper heat-sink 
positions on the component side for on 



92 



board regulators. One position is pre-wired 
and pre-drilled for 7800 series regulators in a 
TO-220 type case. Unregulated power input 
from connector pin one is connected to the 
appropriate regulator lead; regulated power 
is distributed via the power plane on the 
component side. Ground potential is routed 
from connector pin 100 to the plane on the 
wiring side. The second regulator position is 
uncommitted. Provisions are made to cut 
power conductors for special applications. 
One low profile, finned heat-sink is supplied 
with each board. 

The 5.313 inch by 10 inch (13.5 cm by 
25.4 cm) boards are manufactured of blue 
0.06 inch (1.52 mm) FR-4 epoxy glass 
material. Two ounce 0.0028 inch (0.07 mm) 
thick copper foil pattern has solder plating 
for conductors and gold-flashed nickel 
plating for connector contacts. The card has 
100 (50 each side) connector fingers spaced 
on 0.125 inch (0.318 cm) centers. Holes are 
provided for card ejectors. 

The 8800 V boards, priced at $19.95 
(1-4), are available off the shelf from Vector 
Electronic Company Inc, 12460 Gladstone 
Av, Sylmar CA 91342, or through 92 
distributors in the United States and Canada. 
Full size layout sheets showing hole and bus 
location are provided with each board." 



Introducing 

A New and Unique 

Computer Graphics Terminal 

To Fit Your Altair 

* B+W Matrix of 128 Horizontal x 192 
Vertical Dots 

* 3K x 8 No Wait, Static RAM, ON BOARD 

* Light Pen And Control Panel Included 

* Bandwidth is Compatible with standard TV 
Set 

* Output is 2.25V PP Video 

GDT-1 is a 2 slot Altair plug-in graphics 
terminal that generates 24K dots on a 
standard B+W TV set. Unit displays data 
stored in on board 3K x 8 memory, which is 
fully computer accessible. Control panel 
allows data to be entered by light pen or 
computer. 

Kit $185., Assembled $235 

Computer graphics, Associates 

56 Sicker Road 
Latham, N.Y. 12110 

N.Y. Res. add Sales Tax - Add $2.00 Shipping 
Send $1.00 for Data Pkg. 



S.T.M. SYSTEMS 
Not a Kit Presents Fully Tested 

BABY! 

A complete microcomputer in an attache case. 

The unit uses the MCS 6502 8 Bit Microprocessor. 

Up to 4K RAM fully buffered * Slot for 4K ROM 

(2708 type) 

DMA, Video Interface (composite video) sixteen 32 

character lines. 

Audio cassette Interface (data rate approximately 1200 

BPS load 8t dump). 

I/O ports with 1 PI A 6820, 6520 type. 

Typewriter type 63 key keyboard, (upper and lower 

case plus Greek with control key). 

Power supply 120 VAC to 5 volt 3 amp fully regulated. 

Speaker, two (2) LEDs, DMA, 60 Hz real time clock, 

video on and off keyboard and audio cassette dump 

and load format all under program control. 

The first 200 systems sold will have a frosted Plexiglas 

case! Standard unit will have molded plastic case, 

Plexiglas case will become an option. 

Audio cassette tape supplied with dump program, text 

editor, games of Shooting Stars, Life and Ticktack Toe, 

Music Program (self generated computer music and 

user generated from keyboard). 

* Basic unit with 2K RAM and 512 Byte bootstrap 
loader and monitor in firmware (PROM) ... $ 850.00 

Unit with 4K RAM $1000.00 

Remember it's not a kit, it's fully tested and ready to 
go. Just plug BABY! in hook up your video monitor, 
load your auto cassette with the programs we supply 
and you're off and running. 
Option Video Monitor $150.00 

Be the first person on your block to have this unique, 
completely portable system. 

ORDER TODAY: 
S. T. M. SYSTEMS 

P.O. Box 248 
Mont Vernon, N.H. 03057 



D BankAmericard Exp. 
IZI Master Charge No. 



DCashier's Check 

D Money Order 

Personal Check (allow 6—8 weeks for personal check to clear.) 
Delivery 60 to 90 days after Receipt Of Order 

Name 



Address 
City 



State 



Zip 

Ask for our OEM discounts on customized version. 
See write-up on page 122 of this issue. 



93 




PRIZES 

Grand prize winner will receive, in 
addition to the fame of having his 
entry appear on the cover of the 
December 1976 issue of BYTE, 

• $100 

• A lifetime subscription to BYTE 

• A bound volume of BYTE 
Volume 1. 

Two runners up will receive $100 and 
a five year subscription to BYTE. 
Five honorable mention winners will 
receive a tee shirt wardrobe (one from 
Creative Computing, one from Com- 
puter Lib, and one from BYTE) and a 
one year subscription to BYTE. 




COMPUTER ART CONTEST 

BYTE announces a contest for art- 
work suitable for use on the cover of 
BYTE Magazine. Entries can either be 
artwork created by a computer or 
human produced artwork on a com- 
puter theme. 

All entries become the property of BYTE 
Publications but will be returned if accom- 
panied by a self addressed stamped enve- 
lope. Though only one grand prize winner 
will be chosen to appear on the cover of the 



December 1976 issue of BYTE, any entries 

which the BYTE staff like well enough to 

use as covers will be purchased at our usual 

rates. 

All entries must be received by August 31 

1976. 



Mail to: 

Ms Janice Black 

Contest Editor 

BYTE Publications Incorporated 

70 Main Street 

Peterborough NH 03458 



94 



Functional Specifications: 

An electronic device or computer pro- 
gram is defined by a "functional specifica- 
tion" detailing what it is to do. In a similar 
vein, here are functional specifications of 
two articles which should appear in future 
issues of BYTE — the rewards to the writers 
of the articles selected will be publication in 
BYTE (fame) and our top payment rate at 
the time of publication (fortune). 

Direct Digital Recording — Theory and 
Practice 

An individual with experience in de- 
sign and implementation of magnetic 
recording interfaces is sought to supply 
an article on the design and practical 
implementation of electronics to drive a 
digital magnetic recording head in an 
output mode and decode the input from 
that head in a read mode. Background 
material might include definitions of the 
various industry standard recording 
methods, and selection of one such 
method for a detailed circuit which can 
be used by the individual experimenter. 
The circuit designed should include gener- 
ation and decoding of the data format 
from a parallel data word read or written 
by a microprocessor following an inter- 
rupt signal. The article should be accom- 
panied by photographs of the prototype, 
photographs of oscilloscope traces indi- 
cating circuit timing, and rudimentary 
software for an existing microprocessor 
to illustrate testing and alignment as well 
as normal data read and write operations. 
The rationale for this function is that it 
will enable readers to use surplus tape 
drives or disk drives by the strategy of 
ripping out the old (undocumented) elec- 
tronics and installing new interfaces from 
the head outward. It will also allow use of 



new equipment purchased without head 
interface electronics. 

Serial File Systems — Theory and 
Practices 

An individual with experience in the 
design and implementation of file man- 
agement systems for serial recording 
media with electronic control is sought to 
supply an article or articles on the sub- 
ject. The goal is to define what is meant 
by a "file," concepts such as naming, 
directories, search strategies, record for- 
mats, etc. The goal is a functional specifi- 
cation of utility software which can be 
implemented for any microprocessor with 
appropriate detailed code. The program 
specifications should be made either in 
the form of flow charts or structured 
"pseudo code" (see Ronald T Herman's 
article on page 22 of June 1976 BYTE). 
The article should be accompanied by 
illustrations to document data formats 
and other details. The rationale for this 
function is that given an electronically 
controlled tape drive, the individual 
experimenter will be able to take this 
software specification and implement a 
system to create, update and delete 
named files. 

The purpose of stating these specifica- 
tions is to encourage work in these areas, 
work which will be of great utility to our 
readers. Our intention is to publish at least 
one high quality article on each subject as 
soon as possible. Remember that with few 
exceptions, BYTE authors are not pro- 
fessional writers, but are instead experi- 
menters (professional or amateur) in the 
computing field who record the results of 
their efforts in the form of manuscripts 
submitted to BYTE. ■ 



SOLID STATES MUSIC PRODUCTS 



Static Memory Boards (4Kx8) 
MB-1 Mk-8 Board 
Kit $1 03 PC Board $22 

MB-2 Altair 8800 board with on board 
address & wait switching. 

Kit(2102's 1us) $112 

Kit(91 L02A's) $139 PC Board $25 



Erom Board 

MB-3 EROM Board with on board ad- 
dress and wait switching. 2Kx8 may be 
expanded to 4Kx8 

2K Kit $145 4K Kit $225 

Kit Less EROMs $65 



I/O Boards 

1/0-1 8 bit parallel in & out ports 
Common address decoding jumper se- 
lected, Altair 8800 Plug compatible. 
Kit $42 PC Board $25 

I/0-2 I/O for 8800, 2 ports committed 
pads for 3 more, other pads for EROMs, 
UART, etc. 
Kit ... $47.50 PC Board $25 

Misc. 

Altair compatible mother board . . . .$45 

32x32 Video Board $35 

Altair extended board (less con.) . . . .$8 



2102's 



1usec 



.65usec 



.5usec 



ea. 
32 



$1.95 
$59 



$2.25 
$68 



$2.50 
$76 



8212 


$5.00 


1 702A* 


$10.00 


MM5320 


$5.95 


2101 


$ 4.50 


AY5-1013 UART 


2111-1 


$ 4.50 




$7.95 


2112 


$ 4.50 


74200 


$5.90 


8223 


$ 3.00 


74L200 


$5.90 


91L02A 


$ 2.55 


MH0025 


$2.50 


32 ea. 


$ 2.40 


MH0026 


$2.95 


'Programing send 


8T97 


$2.10 


Hex List 


$ 5.00 


Please sen 


d for com 


plete listing of IC's and 


Xistors at competitive prices. 





MIKOS 

419 Portofino Dr. 
San Carlos, Calif. 94070 

Check or money order only. Calif, residents 6% tax. All 
orders postpaid in US. All devices tested prior to sale. 
Money back 30 day Guarantee. $10 min. order. Prices 
subject to change without notice. 



95 



Interfacing the 

60 mA Current Loop 



Walter S King 

451 -145th Place NE 

Bellevue HA 98007 



TT~~f 



32 



KEYBOARD 



/77 



Generally the older Teletype units such as 
model 15s, 19s and 28s require a 60 mA 
loop to operate the printer. These older 
machines are not as attractive looking as the 
newer model 32s and 33s, but for the Altair 
computer hobbyist, looks are probably 
second to costs. The 60 mA interface cir- 



I2VDC 



T4.BV 
TzENER 



D>^ 



■RSI TO UART 



Figure 1: Input Circuit. The Teletype generates Baudot codes mechanically 
by activating switch contacts according to the code being generated. To 
condition the inputs for the UART, this circuit will debounce the signal and 
convert it to a TTL level. 



cuits shown below are simple, straight- 
forward, and do an effective job. 

Circuit Notes 

The loop keying transistor, 2N5655, is a 
250 V power tab purchased at two for $1 at 
a surplus house. In the mark state, this 
transistor is fully saturated. The collector 
dissipation is 0.7 V x 0.060 A or 0.042 W. In 
the space state, with no collector current, 
the dissipation is zero. Heat sinking is not 
required. The 0.1 /iF and the 470 ohm 
resistor protects the keying transistor from 
voltage spikes generated by the inductance 
of the printer magnet. The 10 K ohm re- 
sistor in base circuit limits the current 
supplied by the UART TSO output gate to a 
safe value when in the mark state. The 
variable resistor in the loop should be 
adjusted with a milliampere in the circuit. 
Set the loop current to 60 mA. A pull up 
resistor, 1 k ohm, is connected to the 
keyboard and +5 V to generate a TTL level 
keying signal. The 1 juF capacitor in parallel 
with the keyboard is used to smooth out any 
contact bounce. The 4.8 V zener diode 
clamps the space signal to 4.8 V (logic I). 
Also, hopefully, it will act as a crowbar 



Figure 2: Printer Drive Cir- 
cuit. The 60 mA current 
loop is a circuit which 
normally passes 60 mA 
through all the printer 
magnets and keyboard 
contacts of Teletypes 
which are "in the loop. " 
This circuit drives the 
printer mechanism only by 
using a TTL level signal 
from the UART to control 
a transistor switch. 




I 



45 
>> 



PRINTER 
MAGNET 



>F 



400 VDC 
470 
/2W 



PHYSICAL 
LAYOUT 
OF 2N5655 



-METAL 
FACE 



I 



Rl 
2K 
OW 



I30VDC 
LOOP 
POWER 
SUPPLY 



T 



96 



120 VAC 
60 Hz 



2A 



Sh 



circuit (short to ground) if high voltage were 
to appear in the keying circuit by accident. 

External Connections 

It is a good idea to mount the keying 
transistor on a perforated board separated 
from the serial 10 board. An inadvertent 
short circuit to the high voltage loop could 
wipe out the serial 10 board integrated 
circuits. The keyboard contacts on a Model 
15 or 19 are usually terminals number 32 
and 34. The printer magnet terminals are 
numbers 46 and 45. If there is a line relay in 
the machine, remove it and discard it. 

UART Connections 

If you are using a Model 15 or Model 19, 
the Baud rate is 45. The UART clock preset 
count for 45 Baud is 2454 in octal. The 
Model 28 with 100 word per minute gears 
runs at 74.2 Baud. The preset count for 74.2 



Figure 3: To complete the adaptation of a 60 mA TTY to your UART, this 
simple power supply will provide the necessary voltages. The transformer 
should have a secondary with at least 90 volts AC input to the bridge 
rectifier. The actual value could be 90 to 120 volts or so depending upon 
what you can find in the junk box of your home laboratory. The capacitor 
value of 1 750 pF is also not critical. The voltage rating should be higher than 
the output peak of the bridge rectifier and the value should be greater than 
500 fiF. 

Baud is 4553 in octal. Since these older 
Teletypewriter machines use only five data 
bits, the UART jumpers NDBI and NDB2 
must be wired to GND. The NSB jumper is 
connected to logic 1 which selects 1-1/2 stop 
bits when NDB1 and NDB2 are grounded. 

If read errors begin to occur on the 
keyboard, it is probably due to an oil film 
on the keyboard switch contancts. Use a 
little carbon tetrachloride solvent on them 
or carefully pull a piece of paper between 
the contacts to clean them." 






p 




101 BASIC Computer Games is the most popular 
book of computer games in the world. Every pro- 
gram in the book has been thoroughly tested and 
appears with a complete listing, sample run, and de- 
scriptive write-up. All you need add is a BASIC- 
speaking computer and you're set to go. 

101 BASIC Computer Games. Edited by David H. 
Ahl. 248 pages. 8V 2 x11 paperbound. $7.50 plus 75d 
postage and handling ($8.25 total) from Creative 
Computing, P.O. Box 789-M, Morristown, NJ 07960. 



j2 Gmw 


Mil Description 






C ACEYQU 
<D AMAZlN 




mo 


Try lo hit ihe mystery jackpot 


Play aceyducey wild Ihe compute' 


HI 4 


Try to remove all (he pegs Irom a board 


Computet construct a maze 


HMRABI 


Govern the ancienl city-stale ol Sumer ia 


"£= ANIMAL 


Computer guesses animals and learns new 


HOCKEY 


IceHrxkeyvs Cornell 


o 


ones From you 


HORSES 


OH-ttack belting on a horse race 


V AWARI 


Ancienl game ol totaling beans in pus 


HURKLE 


Find the Hurkle hiding on a 10 1 10 grid 


U BAGLES 


Guess a mysiery 3-digil number tiy logic 


KINEMA 


Drill in simple kinematics 


. BANNER 


Pi mis any message on a large banner 


KING 


Govern a modern island kingdom wisely 


i. BASBAL 


Baseball game 


LETTER 


Guess a mystery tetter - computer 


■L BASKET 


Basketball game 




gives you clues 


V BATNUM 


Match wits in a bailie ol numbers vs 


lift 


John Conway's Game ol Lite 


m 


the computet 


UFE-2 


Compeiiiive game ol lite 1 2 or more 


mm BATTLE 


Decode a matr ii to locate enemy 




playttsl 




battleship 


LITQ2 


Children's literature qui/ 


BINGO 


Computet prints yout card and calls 


MATH01 


Children's arithmetic drill using 




the numbers 




pictures ol dice 


BLKJAC 


Blackiack Ivery comprehensivel. Las 


MNOPLY 


Monopoly Itx2players 




Vegas rules 


MUGWMP 


Locate 1 Mugwumps hiding on a 10 i 10 


BLKJAK 


Blackiack | standard game) 




grid 


BOAT 


Destroy a gunboat Irom your submarine 


NICOMA 


Computer guesses number you Hunk ol 


BOMBER 


F ly World War 11 bombing missions 


HIM 


Chinese game oINim 


BOUNCE 


Plot a bouncing ball 


NUMBER 


Silly numbet matching game 


BOWL 
BOXING 


Bowling al Ihe neighborhood lanes 
3-tound Olympic boxing match 


1 CHECK 


Challenging game lo remove checkers 
Irom i board 


BUG 

6ULC0W 


Roll dice vs the computer to draw a bug 
Guess a mystery 5-digil number vs 


ORBIT 


Destroy an orbiting germlaiden enemy 
spaceship 


BULEYE 
BULL 


Ihe computet 
Throw dans 
You're the matador in a championship 


PIZZA 

POFTRY 


Deliver pmas successfully 
Computer composes poetry in 4-part 
harmony 


BUNNY 


bull light 

Computer drawing of the Playboy bunny 


POET 
POKER 


Computet composes random poetry 
Poker game 
3-dimensional liciac toe 


BUZZWD 


Compose your speeches with the latest 


OUBIC 


CALNOR 


buz Avoids 
Calendar loi any year 


QUEEN 


Move a single chess queen vs Ihe 

computet 
Order a series ot numbers by reversing 


CAN -AM 


Dnve a Group 7 car in a Can Am load race 


REVHSE 


CHANGE 


Computer imitates a cashier 


ROCKET 


Land an Apollo capsule on the moon 


CHECKR 


Game ol checkers 


R0CKT1 


Lunar landing horn 500 leet 1 with plot) 


CHEMST 


Dilute kryplocyanic acid lo make n 


R0CKT2 


Very comprehensive lunar landing 




harmless 


ROCKSP 


Game ol rock, scissors, paper 


CHIEF 


Silty arithmetic drill 


ROULET 


European roulette table 


CHOMP 


Eal a cookie avoiding Ihe poison niece 


RUSROU 


Russian roulette 




12 or moreplayersl 


SALVO 


Destroy an enemy Heel at ships 


CIVILW 


Fight ihe Civil Wat 


SALVO i 


Destroy 4 enemy outposts 


CRAPS 


Play craps Idicel. Las Vegas style 


SLOTS 


Slot machine lone aim bandit 1 


CUBE 


Negotiate a 3-0 cube avoiding hidden 


SNOOPY 


Pictures ol Snoopy 




landmines 


SPACWR 


Comprehensive game ol space war 


OtAMND 


Prints 1 page diamond patterns 


SPLAT 


Open a parachute at the last possible 


DICE 


Summaries dice rolls 




moment 


DIGITS 


Computer tries lo guess digits you 


STARS 


Guess a mystery number - stars give 




select at random 




you clues 


DOGS 


Penny arcade dog tace 


STOCK 


Stock market simulation 


EVEN 


Take objects f torn a pile - try lo end with 


SYffONM 


Word synonym drill 




an even number 


TARHT 


Destroy i targel in 3-0 space- 


IVENI 


Same as EVEN - computer improves 




very tricky 




its play 


30 PLOT 


Plots families ol curves- looks 3- 


FIFTOP 


Solitaire logic game - change a row 




dimensional 




olXsloOs 


TICTAC 


Ticlac'loe 


FOCTBL 


Professional tootball 1 very comprehensivel 


TOWER 


Towers ol Hanoi punle 


FOTBAl 


High School football 


TRAIN 


Time-speed distance quti 


FURS 


Trade luts wilh the while man 


TRAP 


Trap a mystery rumbei -computer gives 


GOLF 


GdII game -choose your clubs and swing 




you clues 


G0M0KO 


Ancenl board game at logic and strategy 


23MTCH 


Game at 23 maiches - try not to take 


GUESS 


Guess a mystery number - computer 




the last one 




gives you clues 


UGLV 


Silly pralile plot ol an ugly woman 


GUNNER 


Fire a cannon al a stationary targel 


WAR 


Card game of war 


GUNERI 


F ue a cannon a! a moving target 


WAR-2 


Trooptaclrcsmwar 


HANG 


Hangman word guessing game 


WEKDAY 


Facts about your birthday 


HELLO 


Cempuler becomes your friendly 


WORD 


Woid guessing game 




psych i at n si 


YAHTZE 


Dice game olYahtiee 


HEX 


He«apawngame 


ZOOP 


BASIC programmer's nightmare 



o c 

(f 
o c 
o c 



o c 


CL 



97 



What's 

New? 



Build This Printer Kit 

Southwest Technical Products has just 
announced a new printer kit which provides 
an economical hard copy option for personal 




systems users. The kit, shown assembled in 
the photograph, contains a mechanism and 
drive electronics. The mechanism of this 
product is an OEM printer of a type widely 
used in "point of sale" terminals and elec- 
tronic cash registers. Since it was designed 
for mass production and rugged commercial 
use, the mechanism is inexpensive and will 
probably prove to be quite reliable in the 
home environment. 

The printer produces a 5 by 7 dot matrix 
character with 40 characters per line. The 
maximum rate is quoted as 75 lines per 
minute (multiplying out gives a character 
data rate of 3000 characters per second). 
The drive electronics includes a 40 character 
line buffer; printing begins automatically if 
the buffer is full, or whenever a carriage 
return character is sent. The character set is 
a six bit ASCII subset with 64 characters. 

The printer is only available in kit form, 
and includes the assembled print mechanism, 
chassis, circuit boards, components, 120/240 
VAC 50 or 60 Hz power supply, assembly 
instructions, one ribbon, and one roll of 
paper. It sells for $250 postpaid in the USA, 
and delivery is quoted as 30 days after 
receipt of order. Contact Southwest Techni- 
cal Products Corporation, 219 W Rhapsody, 
San Antonio TX 7821 6." 



OEM Floppy System Kit 

One of the major subsystems which the 
complete small system must have is an 
electronically addressable mass storage de- 
vice. One solution to this requirement which 
will be within reach of many amateurs is a 




floppy disk subsystem. For those who do 
their own interfacing and are not afraid to 
wire up a parallel port, this "OEM Floppy 
System Kit" from Sykes Datatronics Inc 
should prove to be an excellent subsystem 
assembly. It is designed to be sold to 
electronic engineers in the same way that the 
various OEM oriented microprocessor evalu- 
ation boards are sold, which is why there is a 
package available in quantities of one which 
the advanced amateur can use. 

Here is what you get: The kit consists of 
a smart disk controller for either IBM 
compatible or dual density formats, capac- 
ity for one, two, three or four daisy chained 
disk drives (one comes with the kit), inter- 
connecting cables from the controller board 
to the disk drives, and a hardware interface 
for connecting the floppy system to micro- 
computers. 

The controller itself is packaged on a 
single printed circuit board which mounts 
directly on the disk drive. The controller 
provides hardware versions of functions 
which are often done in software, including: 
hardware address search, automatic sector 



98 



and track sequencing, an asynchronous first 
in first out (FIFO) buffer, and automatic 
cyclic redundancy check generation and 
detection. In the dual density format mode, 
the controller writes 630 K bytes per 
diskette, and in the IBM compatible format 
mode, the controller writes 256 K bytes per 
diskette. 

The microcomputer 10 interface of this 
controller is an 8 bit bidirectional bus whose 
logical configuration is similar to a micro- 
computer memory element. Only 13 parallel 
lines are required for the complete interface 
to transmit data, disk commands and disk 
status information. The typical interface will 
require only 6 to 8 integrated circuits in the 
microprocessor to generate the control 
signals. 

As an example, one PIA port on the 
typical 8 bit microcomputer has 16 bidirec- 
tional data lines plus programmable control 
lines, which should be more than adequate 
to drive this interface through relatively 
short cables. The price for a single drive kit 
in single quantity is $1398. OEM quantity 
discounts are also available, so full service 
computer stores might find this an attractive 
package as well. Sykes Datatronics Inc is 
located at 375 Orchard St, Rochester NY 
14606 (71 6)458-8000." 



8,192 x 8 BIT STATIC MEMORY 
EXCEPTIONALLY LOW POWER 




KIT $325.00 SPECIAL THIS MONTH ONLY $295.00 

* ALTAIR 8800/ IMSAI 8080 BUS COMPATIBLE 

* FAST 215 nS- FULL SPEED- FOR Z80 ALSO 

* EXCEPTIONALLY LOW POWER - LESS HEAT 

* LESS THAN OTHER "LOW POWER" MEMORY 

* BATTERY STAND-BY CAPABILITY 

* ALL SIGNALS TO MOS DEVICES BUFFERED 



PROTOTYPING BOARD 
EXTENDER CARD 
HEX/OCTAL ENCODER 



LOW PROFILE IC SOCKETS 

EDGE CONNECTORS 

DB25 CONNECTORS 



NJ RES. ADD 5% SALES TAX. SHIPPING EXTRA, ADD $2.00 

ALL PRICES & SPECIFICATIONS ARE SUBJECT TO 
CHANGE WITHOUT NOTICE. PRICES ARE USA ONLY. 

ELECTRONIC CONTROL TECHNOLOGY 
P.O. BOX 6 UNION, NJ 07083 



'iStf'T It TTNVE YJJJ 
OHDERXP SotKfl 

CREATIVE 

CaMPLITJNG 
STUFF!! 



Creative Computing 
Magazine 

A bi-monthly 88-page magazine for students, 
hobbyists, and anyone curious about computers. 
Fiction, articles, humor about computers, 
cybernetics, careers, building info., etc. Emphasis 
on games, puzzles, and projects. Contemporary, 
non-technical approach. Subscription. $8.00 pp. 

Games & Puzzles Issue of 
Creative Computing 

88 pages of games and puzzles for pocket 
calculators, computers, and humans. "Beating the 
Game," "Computer Chess," "Hunting a Wumpus 
in a Cave," building your own computer, reviews of 
24 games, books, and much more! $1.50 pp. 

Futures Issue of Creative Computing 

Artificial Intelligence (Bertram Raphael, Herbert 
Dryfus, etc.), Extraterrestrial Intelligence (Isaac 
Asimov, Martin Harwit, etc.), microprocessors, 
videodiscs as an ultimate computer input device, 4 
new games, and more. 88 big pages! $1.50 pp. 

Artist and Computer 

A high-quality, 4-color book edited by Ruth Leavitt 
which displays the work of 35 internationally- 
known computer artists. Each artist describes his 
or her work in non-technical terms. 140 il- 
lustrations. $4.95. 



tOVKC ! 



The Best of Creative Computing 

A 328-page book featuring stories by Isaac Asimov 
and others; articles on cybernetics, robots, 
computer crime, privacy; computer games such as 
Star Trek, Rabbit Chase, Magic Square, Madlib, 
and 14 more; super computer graphics; cartoons, 
reviews; poetry; and more! $8.95. 

Creative Computing T-Shirt 

Albert Einstein portrait produced by Blocpix™ 
process. Scarlet trim, black design. Available in 
adult sizes: S, M, L, XL. $4.00 pp. 

Mr. Spock Computer Image 

Big 17x22" computer scanner image. Heavy stock. 
Comes in strong mailing tube. $1.50 pp. 

Star Trek People Computer Images 

Six 8'/zx1 1 computer images on heavy stock of 
Kirk. Spock, McCoy, Scott, Chekov, and Uhura. 
$1.50 pp. 

101 BASIC Computer Games 

A collection of 101 games in BASIC, each one with 
a complete listing, sample run, and write -up. 256 
pages. $7.50. 



Please send me the following: 
Item 



Price 



Shipping (books only) $1.00 

All orders outside U.S.A. add $1.00 

New Jersey residents add 5% sales tax 

Total ^____ 
DCash, check, M.O. enclosed 

DCharge my Bankcard (minimum charge $15) 

DBankAmericard DMaster Charge 

Acct. No. 



Expiration date. Mo.. 



.Yr. 



Name. 



Address 



City 



State 



.Zip. 



Creative Computing, P.O. Box 789- M, 
Morristown, N.J. 07960, U.S.A. 



99 




Clubs and Newsletters 



Word Processing, Anyone? 

Robert H Edmonds, PO Box 464, 
Estudillo Station, San Leandro CA 94577, is 
interested in applications of personal micro- 
processor systems to word processing. He 
writes: 

/ am interested in microcomputers in 
order to get a word or text processing 
device. I want to be able to write articles 
or letters, type them once, revise and 
then retype them without inputting the 
whole text again. I do not know of any 
special interest group or club that pursues 
this application for the home hobbyist or 
writer. The major economic obstacle is 
the cost of a good output typewriter 
(Diablo or Qume). The audio cassette 
interface makes it feasible for a group of 
people (writers, etc) to get an output 
device with each having his own input 
and editing facilities. Commercial word 
processing equipment is just too expen- 
sive for home use. 

Robert requests that anyone interested in 
this application communicate with him. 

Oregon Computer Club 

An as yet unnamed computer club has 
been formed in Oregon, according to John R 
Lynch Sr, secretary. A naming process is 
currently in progress, and an official consti- 
tution is in the works. Membership as of 



May 4 1976 was 49, with approximately 
40% of the members owning some form of 
computer. The club meets on the last Satur- 
day of the month. For information on time 
and place, contact one of the officers elected 
on March 20 of this year: 

Chairman: Bill Marsh, 2814 NE 40th, 

Portland OR 9721 2. 
Secretary: John R Lynch Sr, 2105 SW 
Wembley Pk Rd, Lake Oswego OR 
97034, phone (503) 636-8598. 
Treasurer: Joseph Bartel, Portland OR. 
Program Director: Mike Boyd, Milwaukie 
OR. 

Midwest Alliance of Computer Clubs 

The Midwest Alliance of Computer Clubs 
is an association of different clubs in the 
midwest. President is Gary Coleman, 14058 
Superior Apt #8, Cleveland OH 44116, 
(216) 371-9304. Purpose of the alliance is to 
coordinate activities which are beyond the 
scope of any one club. The first major 
activity was a Computerfest held June 11, 
1 2 and 1 3 in the Cleveland suburb of Shaker 
Heights. 

Ventura County Computer Society 

A copy of the Volume 1, #1 issue of the 
VCCS Newsletter came this way recently. The 
president of the society is William B Cowley, 
4240 Harbor Blvd #208, Oxnard CA 93030, 
985-2631 or 982-4783. The newsletter re- 
ported a hardware buildup group working, on 
a bit slice version of an Altair/IMSAI CPU 
board and a business group discussing ap- 
plications to commercial activities of mem- 
bers, among other activities. And of course 
there is the ever present group purchase 
operation. 

NASA-JSC Computer Hobbyist 
Club (Houston TX) 

The NASA-JSC CHC was formed on 
November 5 1975. Circa April 16 1976, the 
club consists of some 30 members and is 
sanctioned by the NASA Employees Activ- 
ity Association. The group ranges from 
interested novices to computer experts. 
Many of the members, according to Marlowe 



100 



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^ Computing 



76 



Consumer Trade Fair 



Atlantic City, N.J. 
August 28th-29th 



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r What its all about! 

Software Development 

Micro Computers 

Hardware Development 

Disc Memories 

Computer Comparisons 

Interfacing 

Program Implementation 

AMSAT 

Computerized Music 



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Video Terminals 

Kit Construction 

Printers 

Computer Games 

Digital Tapes 



i;* s :: ' :i i-.iefTi'maWafra Technical talks by leading electronic equipment manufacturers 

• Major Exhibits from all over the country 

• Demonstrations in many areas including Home and Personal Computing 

• Door Prizes, Free Literature and Free Mementos 

• All this plus Sun and Surf - Fun and Excitement - Relaxation and Leisure 

Weekend Fair admission $5.00 advanced. $7.50 at door ! : 
Admission includes Exhibits, Seminars 

Write for FREE TRIP-KIT to Personal Computing 76 Fair Headquarters Shelburne Hotel-Motel 
Box 1138 Boardwalk and Michigan Ave. Atlantic City, New Jersey 08404 
EXHIBITION BOOTHS STILL AVAILABLE - CALL (609) 927-6950 



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Cassetti [1011 Devonport Ln, Seabrook TX 
77586, (713) 474-2923] have either a micro- 
computer or plans to acquire one. Meetings 
are twice a month at the JSC recreation 
center, and feature a lecture or demonstra- 
tion after a short business meeting. The 
meetings also promote information exchange 
and advice for beginners. Although member- 
ship is limited to NASA employees and 
contractors' employees, guests that share 
this common interest are welcome. For more 
information contact Marlowe. 

Canadian Computer Club 

The needs of Canadian personal com- 
puting hackers have been addressed by the 
new Canadian Computer Club, which has 
published Volume I #1 of a newsletter late 
in March. The newsletter looks like an 
excellent start. For further information 
contact: 

Canadian Computer Club 

c/o G Pearen 

861 -11th St 

Brandon, Manitoba CANADA R7A 4L1 

Phone: (204)725-1079 



Clubs and Newsletters Directory 

As a summary of the current state of local, regional, and national 
organizations, special interest groups, and periodicals of interest to 
personal computing people, BYTE will publish a directory in a 
forthcoming issue. We would appreciate it if each such organization 
would provide a summary of applicable information in the following 
list: 



• Name of organization [eg: Silicon Hollow Computer Coven] . 

• Mailing address [eg: PO Box 31, Silicon Hollow, Transylvania 
00000] . 

• Meeting location [eg: Third stump past the 1 1th sinkhole on the 
old Silicon Hollow game trail] . 

• Meeting algorithm [eg: "First Tuesday after the second Wednes- 
day before the first full moon of leap years"] . 

• Name of newsletter or publication [eg: Silicon Boule]. 

• Contact person [eg: Witch Hazel]. 

• Contact phone number. 

• Dues or subscription fees. 

• Special interests [eg: Computer applications: the automated 
swamp] . 

• Other comments. 

The deadline for the directory information is September 15 1976. If 
you wish to be certain that the latest information about your club, 
newsletter or organization is available, be sure to send this information 
to 

BYTE 

Clubs & Newsletters Directory 

70 Main St 

Peterborough NH 03458 



Amateur Radio ASCII Petition 

Bruce J Brown, WB4YTU, 4801 Kenmore 
Av #1022, Alexandria VA 22304, 
(703)370-1431 home, (202)697-9654 work, 
sent BYTE a copy of a "Petition for 
Rulemaking" recently submitted to the 
FCC. It is highly desirable to have ASCII 
radio transmission allowed on amateur bands 
in order to continue the exploration of radio 
data communications between hackers. Indi- 
viduals who are interested in pushing 
through FCC rule changes for that purpose 
might contact Bruce to get a copy of his 
petition, and possibly help out in the effort. 

Beverly Hills High School Club 

The Beverly Hills High School Computer 
Club invites guest speakers to come and give 
talks on computers and the computer in- 
dustry. Anyone willing to volunteer a talk to 
this group of eager students is urged to 
contact Kwok-Fung Yen, vice president, 
Beverly Hills High School Computer Club, 
241 Moreno Dr, Beverly Hills CA 90212. 

University of Florida Club 

The first meeting of the University of 
Florida's Amateur Computer Society was 
held April 14 in the J Wayne Reitz Student 
Union on the campus. Aside from organiza- 
tional trivia, the first session featured an 
Altair 8800 system demonstrating the AM 
radio peripheral, and a talk by a member of 
the Human-Dolphin Foundation on the use 
of computers in man-dolphin communica- 
tions work. A permanent mailing address has 
not yet been established. For the time being, 
the contacts are: 

University of Florida Amateur Computer 

Society 
c/o Steve Ackerman or Ken Massey 
Electrical Engineering Department 
Room 234, Larsen Hall 
Gainesville FL 32611 

ACM Seventh US Computer 
Chess Championship 

Entries are being solicited for the Seventh 
US Computer Chess Championship to be 
held October 19 to 21 1976 in conjunction 
with the ACM Annual Conference in the 
Hyatt Regency Hotel, Houston TX. A four 
round Swiss style tournament is planned 
with the first round on Tuesday, October 
19, beginning at 8 PM, and the final round 
on Thursday, October 21 , at 8 PM. The field 
will be limited to 12 teams. David Levy, 
International Master from England, will 
serve as tournament director. 

For further information and for an appli- 
cation form, write to Dr Monroe Newborn, 



102 




BYTE UNDER GLASS 

Paul Terrell, founder of the BYTE Shop, the world's first computer store franchise, puts 
lock and key to "the family jewels." Each BYTE Shop Computer Store has on display, as a 
distinguishing mark of its identity, BYTE magazines under glass. The BYTEs were placed under 
glass as a result of an unfortunate rip off of issue number one after a BYTE subscription ad 
entitled "A Lesson in Economics" mentioned that number ones were selling for $15. 

Though current issues of BYTE are not yet as rare as the first few, they soon will be, as we 
do not print a large overrun. Don't miss any. Subscribe today. Use the pull out card in this issue 
or the coupon below. 

****** SPECIAL ****** 

Subscribe to BYTE and Creative Computing and save $2. 

Since we feel that you really need both magazines to be fully informed in the small systems 
field, the publishers are offering a special package. Receive one year of both BYTE and Creative 
Computing, normally $20, for only $18. A ten percent saving. 
Please enter my subscription to: 



□ BYTE 1 year $12, 2 years $22, 3 years $30 (circle one) 

□ BYTE and Creative Computing 1 year $18, 3 years $46 
d Check enclosed 

□ Bill me 

□ Charge to MC# BAC# . 

Exp. date 



Name . 



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City 



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Please allow six weeks for processing. 



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103 



School of Computer Science, McGill Univer- 
sity, Montreal, Quebec H3C 3G1, CANADA. 

A Newborn Newsletter 

A newborn self published newsletter has 
been announced in a letter to BYTE. It's 
called The Circular File and volume 
number is a flier discussing its purpose. 
The planned length is 10 pages, and informa- 
tion will be from user submissions of camera 
ready copy. The price is $5 for 1 2 issues, for 
a total of 1 20 pages at the 1 pages per issue 
size. User cost, delivered, is thus 4.17 cents 
per page. 

Planned topical areas will be letters, 
editors commentary, programmable calcula- 
tors, microprocessor systems, and notices of 
swaps or surplus items for sale. 

For information, and to submit materials, 
contact: 

The Circular File 
Marc Cobert 
201 3 East 1 2 St 
Brooklyn NY 11 229 

Westchester-Fairfield 
Amateur Computer Society 

BYTE received an existence proof of the 
Westchester-Fairfield Amateur Computer So- 
ciety in the form of an announcement for 
the May 6 1976 meeting which was held at 
the Greenburgh Public Library, Elmsford 
NY. Contact people are: Hal (914)967-7853, 
Carl (914)686-1318, and Don 
(203)348-1627. 

New England Computer Society 

The Volume 1 #6 issue of the NECS 
Newsletter included a continuation of Jeff 
Millar's comments on local (eastern Massa- 
chusetts and southern New Hampshire) sur- 
plus stores, an article on MIKBUG by John 
Watson, a cassette interface by Holger Denk 
and a listing of local suppliers' names and 
addresses. The mailing address of the NECS 
is 

New England Computer Society 
PO Box 1 98 
Bedford MA 01 730 

Meetings are held on the first Wednesday 
of each month, at 8 PM at the MITRE 
Corporation plant in Burlington MA. The 
meetings are in the cafeteria, Building C. 

At the May meeting of NECS, the main 
topic of the evening's talk was a presentation 
by some Innovex engineering people on the 
workings of floppy disk drives. Also tried for 
the first time was a version of the Homebrew 
Computer Club's "mapping/random accesss" 
method of meeting organization which made 



quite an impression on a certain magazine 
editor in a recent trip to the west coast. 

New Hampshire Computer Club 

Meeting the second week after the NECS 
get togethers each month (ie: third Wednes- 
day of each month) is a totally informal club 
called the New Hampshire Computer Club. 
Membership is instant and permanent upon 
coming to the first meeting. No dues. No 
newsletter. Lots of interesting talk in a 
round table on technical subjects. The meet- 
ings are at approximately 7:30 - 8:00 PM 
gathering time in the auditorium of Sanders 
Associates main building, off Route 3 near 
the Massachusetts border in Nashua NH. The 
May 19 meeting was a long session which 
split two main topics: high level languages 
and tape recording of data. 

New York Computer Club 

The May 1976 issue of the New York 
Amateur Computer Club publication came 
BYTE's way recently. This issue contains the 
bylaws and formal matters as well as infor- 
mation on planned meetings and workshops 
for members. The club's address is listed as: 

New York Amateur Computer Club 
1E 

375 Riverside Dr 
New York NY 1 0025 
AMRAD 

Amateur Radio Research and Develop- 
ment Corporation is the name of an or- 
ganization with a mailing address of 1524 
Springvale Av, McLean VA 22101, according 
to information forwarded to us by its 
president, Paul L Rinaldo, K4YKB, 
(703)356-9818 evenings. The club attracts 
computer oriented radio amateurs from the 
Washington DC area. More than half of the 
club meetings are devoted to amateur com- 
puter topics, according to Paul's May 9 1976 
letter. Meetings are held on the first Monday 
of each month, beginning at 8 PM, at the 
Patrick Henry Branch Library, Maple Av at 
Center St, Vienna VA. Visitors and new 
members are always welcome. Contact Paul 
by radio, phone or mail. 

Eastern Iowa Computer Club 

In phone conversation, Michael Wimble 
of Cedar Rapids I A mentioned the Eastern 
Iowa Computer Club. According to Michael, 
the club has about 50 members, circa May 
19 1976. For further information, contact 
him at: 

6026 Underwood Avenue SW 
Cedar Rapids I A 52404 
Phone:(319)396-5641 . 



104 



Another MITS Store 

Lou Van Eperen, president of the 
Chicago Computer Store, sent BYTE a 
notice about the opening of his retail MITS 
Altair outlet on May 15. The location is 517 
Talcott Rd, Hwy 62, Park Ridge IL 60068." 



Creative Computing Catalog 

David Ahl, publisher of Creative Com- 
puting, has just released the latest Creative 
Computing catalog. This is "a zany 12 page 
tabloid newspaper in the style of the Old 
Farmer's Almanac [incidentally, published 
just up Route 101 from BYTE in Dub/in 
NHj called, appropriately enough, the New 
Creative Computing Catalog." The catalog 
describes various products which Creative 
Computing markets, including: 

• Eighteen books, among them 707 
BASIC Computer Games and Artist 
and Computer. 

• AT shirt with computerized picture of 
Albert Einstein. 

• A variety of computer art prints 
including Mr Spock and abstract art. 

• Descriptions of Creative Computing 
and BYTE magazines. 




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105 



What's 

New? 



It's About Time! 

We were beginning to think nobody 
would pick up on the Signetics 2650 pro- 
cessor, a design which has been "an- 
nounced" since late 1974 but only in the 
past six months or so available off the shelf. 
The 2650 is an 8 bit central processor which 
has 7 on chip registers organized as two 
banks of three registers with the odd re- 
maining register shared between both banks. 
Also on the chip are the stack pointer and 
the program counter, both with 15 bits, for 
a total memory address space of 32 K bytes, 
divided into four pages of 8 K bytes. Most 
direct addressing is done using 13 bits for an 
address within the "current page." The use 
of only 13 bits for direct addressing allows 
the instruction set to have a fairly wide 
range of addressing modes expressed in its 
multiple byte instructions: Register ad- 
dressing (1 byte); immediate addressing (2 
bytes); relative addressing, optionally in- 
direct (2 bytes); absolute addressing for data 
in the current page (3 bytes) with optional 
modes including indexing, indirection, 
indirect auto increment, indirect auto de- 
crement; absolute addressing for branching 
anywhere in address space with optional 
indirection (3 bytes), and single byte opera- 
tions with inherent addressing. [BYTE has 
an article in the works on details of the 
2650.] 

The AMT 2650 

Briefly, what Applied Microtechnology, 
100 N Winchester Blvd, Suite 260, Santa 
Clara CA 95050, has done is to take the 




• •••°T^»#a 



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2650 processor and package it as a single 
board computer system as shown here. The 
result is called the AMT 2650. The single 
card computer system comes assembled and 
tested at $195, with an optional power 
supply in a desk top package running 
$39.95. The following is a quotation from 
the product announcement received at 
BYTE: 

Applied Microtechnology of Santa 
Clara has announced the AMT 2650, a 
low cost completely self-contained 
microcomputer card system employing 
the Signetics 2650 Microprocessor. 
The unit allows the circuit and system 
designer to hand load and debug pro- 
grams using the powerful 2650 instruc- 
tion set; additionally a 62 pin edge 
connector on the card outputs all 
microprocessor functions plus two 
fully buffered TTL compatible output 
data ports for interfacing with the 
user's hardware application. 

The system includes a panel 
mounted on the card that includes 
data/address LED displays, data port 
LEDs and reset. Programs can be single 
stepped instruction-by-instruction for 
program debug. Addresses can be in- 
dependently incremented by hand and 
are automatically incremented after 
each data load. 

The AMT 2650 contains 256 
bytes of RAM (additional RAM, 
PROM, and ROM can be interfaced 
directly via the edge connector). The 
system requires 5 VDC/2A (optional 
power supply available from the 
vendor). 

This processor card from AMT looks like 
an excellent starting point for a computer 
system which can be used to illustrate 
principles of programming and for beginning 
experimentation in computer systems. With 
buffering and expansion of memory capabil- 
ity, it should be possible to start with this 
seed and grow a full blown general purpose 
system with one of the best 8 bit instruction 
sets on the market today." 



Sherlock Ohms Department 

How do you deduce what major com- 
panies are about to enter the personal 
computing field in a big way? Why, scan the 
help wanted pages of your friendly local 
metropolitan newspaper and see who's hiring 
whom in terms of qualifications and ex- 
perience. It's a reliable way to bypass the 
grapevine." 



106 




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side. Short circuit protected, thermal limiting. 
Kit (less case & hardware) $10.95 + 2 lbs shipping. 



,© 




<^ 1 

'READOUTS 



The expertise used to de- 
velop such games as Life 
or Star Trek can be en- 
listed in the development 
of improved medical tech- 
nologies. 



Continued from page 14 

knowing that the only real limitation to its 
use is imagination. It can be bliss. 

It might seem that going home to a 
computer (!) after having to put up with one 
all day would be unbearable, but it is not at 
all the same. There cannot be in a formal 
and regulated atmosphere the same excite- 
ment and individual challenge that exists for 
the personal computer. It is said that the 
greatest challenge to a writer is a blank sheet 
of paper. Well, to the personal computer it 
has to be a blank system memory, plus the 
flexibility of configuring that system to do 
anything that individual desires. 

Personal computing has to be one of the 
most satisfying outlets of the creative 
impulse. 

Richard Sims 
Boston MA 

You're not the only one ever to be 
frustrated by TSO, batch processing and OS 
jCL. The difference between personal com- 
puting and traditional systems is like the 
difference between depending on a railroad 
and having one's own personal transporter. 

PROGRAMS AVAILABLE 

I wanted to write and let you know I'm 
enjoying your magazine; albeit some of the 
articles are too specific and technical. I 
know your job is not an easy one. 

My purpose in writing is this: I live in a 
small town here and (as far as I know) there 
aren't any other computernuts with whom I 
can converse. Anyway, I've built up a pretty 
good library of simple games such as Hi Lo, 
Towers of Hanoi, Button-Button, Nimber, 
Life, Nim, and a few others any of which I 
would gladly share for nothing to anyone 
who asks. (If you write and want to enclose 
a dollar for copy costs it would be appreci- 
ated - if not, I'll still send the programs). 
All my programs are written in 8080 ma- 
chine language for computer and TV Type- 
writer, although they'd probably work 
through a Teletype without any modifi- 
cation. 

Keep up the good work. 

Ron Santore 

1957HuasnaDr 

San Luis Obispo CA 93401 

MEDICAL MICRO IMPLANTS? 

I am a diabetic of 24 years, on insulin 
from the onset of my condition at age 4. My 
21 month old daughter is also diabetic. I 



have an idea that could well benefit her and 
all other diabetics, provided that it gets the 
developmental support that it deserves. My 
theory is that the new electronic marvel, the 
microprocessor, provides us with the ex- 
tremely accurate basis needed for an artifi- 
cial pancreas. 

Although slow by the standards of the 
huge electronic brains, the microprocessor is 
quite fast enough to take the digitally coded 
output from an analog device that would 
test constantly blood glucose levels. This 
would be compared by the processor against 
a preestablished glucose level for the indi- 
vidual patient. The digital result would then 
be used to establish the need for insulin, as 
well as determining the dosage required. This 
digital figure would then be used to control 
the analog amount of insulin administered. 

This would have been impossible six 
months ago, but the state of the art in 
microprocessor technology has advanced so 
rapidly that such a device, with all of its 
speed and accuracy, should be available to 
the diabetic for a reasonable price. 

I will be working on such a theory, 
developing whatever portions of such a unit 
that I can, with the hopes of presenting this 
theory at Personal Computing '76 in August, 
so that its development can be forwarded by 
the experts of the microprocessor field who 
will be in attendance at this show. The 
expertise used to develop such games as Life 
or Star Trek, can be enlisted in the develop- 
ment of improved medical technologies. 

John David Jones Jr 
Co-Chairman, Personal Computing '76 

Microcomputer controlled prostheses are 
an excellent application of this technology, 
an engineering challenge well worth 
pursuing. 

ON HARD COPY AND 
IBMSELECTRICS 

BYTE magazine is getting rave reviews 
and I certainly feel they are well deserved. 
Do keep up the good work. In fact, I have 
two suggestions about how you might fur- 
ther advance your good works. 

I have just obtained a copy of the new 
book by Don Lancaster, TV Typewriter 
Cookbook. It seems to be up to his usual 
high standards for down-to-earth practical 
writing. But, in a book with the letters TV in 
the title, one would hardly expect to find 
much of a section on methods for obtaining 
hard copy. But there is a section which may 
be worth many times the cost of the book. 

On page 218 Lancaster states that "One 
of the best-kept secrets in the computer 



108 



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C. Super low power consumption (1.5 Ma typ.) ^O 

D. Uses latest MOS 17 stage divider IC. IjS^^ 

E. Eliminates forever the problem of AC line glitches. 

F. Perfect for cars, boats, campers, or even for portable 

clocks at ham field days. 

G. Small size, can be used in existing enclosures. 

Kit includes crystal, divider IC, P.C. Board plus all other necessary 
parts and specs. 



MOTOROLA POWER DARLINGTON - S1.99 

BACK IN STOCK! 
Like MJ3001. NPN 80 V., 10A., HFE 6000 TYP. TO-3 case. 
Wc include a free 723C voh. reg. w/iih schematic for a power supply. 
SPECIAL - $1.99 



MOTOROLA RTL IC'S 

Brand new, factory prime. Hard to find, but still 
used in a variety of projects. (See the RTL Cook- 
book by Howard W. Sams.) 



MC724P-59C 
MC725P-59C 
MC764P-49C 
MC767P-69C 
MC771P-49C 
MC775P-89C 



MC780P-89C 
MC785P-49C 
MC787P-89C 
MC788P-49C 
MC789P-59C 
MC790P-89C 



MC791P-69C 

MC792P-59C 

MC799P-59C 

MC9704P-89C 

MC9709P-69C 

MC9760P-69C 



MV-50TYPELED'! 

byUTRONIX 

10 for $1 

Factory Prima! 



3 DIGIT LED ARRAY - 7Se ^lilj 

by LITRONIX ' : 

0L33MMB. 3 MAN-3 Size Readouts In one 
package. These are factory prime, not 
retested rejects as sold by others, 
compare this price! 75c 3 for $2. 



SALE ON CUT LEAD SEMICONDUCTORS 

Leads were cut for PCB insertion. Still very useable. 



1N914/1N4148 100/S2 

1N4002 1 Amp100PIV 40/$1 

1N4745A16V1WZener 20/S1 

EN2222 NPN Transistor 25/S1 

EN2907PNP Transistor 25/S1 

2N3904 NPN Driver Xstr 25/S1 

2N3392 GE Pre-amp Xstr 25IS1 

C103YSCR.800MA.60V 10/S1 



ALL NEW. 

UNUSED. 

SOME ARE 

HOUSE* 



SLIDE SWITCH ASSORTMENT 

Our best seller Includes miniature and standard 
sizes, single and multi-position units. Ail new. 
first quality, name brand switches. Try one pack- 
age and you'll reorder more. Special — 12 lot IT 
(Assort menl) 



DISC CAP ASSORTMENT 

PC leads. At least 10 different 

values. Includes .001 . .01 , .05, 

plus other standard values. 

60 FOR $1 



UPRIGHT ELECTROLYTIC CAPS 

47 mfd 35 V-10/S1 68 mfd 25V-8/S1 
Brand new by Sprague. PC leads. 



RESISTOR ASSORTMENT 

1/4W5% and 10%. PC leads. 
A good mix of values. 200; $2 



pom-! 



# 



1000 MFD FILTER CAPS 

Rated 35 WVDC Upright style with P.C. leads. 
Most popular value for hobbyists. Compare at up 
to S1 19 each from franchise type electronic parts 
stores. S.D. Special * tot $f 



FAIRCHILD BIQ LED READOUTS 

A big .50 inch easy to read character. Now available In eitrw common anode 
or common cathode. Take your pick. Super low current drain, only 5 MA par 
segment typical y0)JR 

FND - 510 Common Anode CHOICE 

FND - 503 Common Cathode $t.50ea. 6for$7.50 



DUAL 741C (5558) OP AMPS 

Mini dip. New house numbered units 

by RAYTHEON. 

4FORS1 



FET'S BY TEXAS INSTRUMENTS — SPECIAL 5 for $1 

tmS-75 but with an internal house number. TO-92 plastic case. N. Channel, 
Junction type PET. 



We do not sell junk. Money back 
guarantee on every item. No C.O.D. 
Texas Res. add 5% tax. Postage 
rates went up 30%! Please add 5% 
of your total order to help cover 
shipping. 

ORDERS UNDER $10 
ADD 75c HANDLING. 



S. D. SALES CO. 

P.O. BOX 28810 
DALLAS. TEXAS 75228 



ORDERS OVER $1 5 CHOOSE 
$1 FREE MERCHANDISE 

FOREIGN ORDERS MUST BE PAID IN U.S. FUNDS 



industry is that all it takes to convert an 
ordinary Selectric I office typewriter into a 
superb hard copy printer is a small handful 
of cheap solenoids (about $30 worth) and 
some simple modifications that in no way 
impair the use of the machine as an ordinary 
typewriter." 

Now I ask you, which would you rather 
be reading this minute, the Teletype 33-ASR 
type font or most any one of the type fonts 
available for the IBM Selectric? Sure, the 
Selectric isn't really cheap. But, I'll bet most 
people would much prefer to spend approxi- 
mately one grand on a Selectric they could 
modify than on an ASR by Teletype. Sure, 
the Teletype also has reader punch but the 
computer hobbyist could settle for cassette 
until he decided if he really needed a reader 
punch and, if he did, that could be added 
without bringing the total cost much above 
that of the 33-ASR. And what would he 
have for his money? Well, he would have 
BOTH a superb typewriter and a superb 
terminal. 

Unfortunately, Lancaster's instructions 
for making the conversion are no more than 
minimally detailed. I suspect I could do it 
except that I have the Selectric II and no 
mention is made of how that might differ 



from the Selectric I he writes about. And, 
Lancaster tells only how to make a printer 
(not an input device) from a Selectric. He 
concludes with the obvious statement that 
"... low-cost hobbyist conversion kits are 
not yet available, although they are an 
obvious and desirable product." 

My point here is that such a kit would 
quickly appear if a publication such as 
BYTE arroused interest in it. How about it? 

Dr James K Lang 

5 Beech Ln 

Edison NJ 08817 

Let's put it this way: Such a kit would 
sell like hotcakes, due to the ubiquitous 
presence of IBM typewriters. When some 
reader comes up with a practical article on 
how to do it, the article will get the red 
carpet treatment. 

DECEIVED? 

I feel that in some of your articles you 
have deceived your reader. In most cases 
where the 6800 and 8080 are compared, the 
fact that the 6800 addresses 10 devices like 
memory is stated as an advantage. Of course, 
this type addressing of 10 is an advantage in 



THIS IS DJR CDPYDflT CDPYCflT 

HER NAME IS TCHEBYCHEU _._ 




This month we are offering a I IllZit to the first 
to correctly guess what our Copydat Copycat is doing. 
The prize: your choice of one of our PC cards listed 
below. (Hint: it's related to our newest product line, 
the COPYDAT blueprint copiers.) Next month we 
print the answer and the prizewinner. Send in your 
guess today! 



The "old standby" line of Hardware Assemblers: 



CDA 1.1 

CDA2.1 
CDA 3.1 

CONNECTOR 



4KX8 Memory Matrix Prototyping Card for 2102 - 2602 -9102 Static RAMS. 7" x 9", predrilled wire 
wrap custom decoding area and plated-through holes in RAM area. $34.95. 

General Purpose Prototyping Card, predrilled for wire-wrap, pictured in BYTE Dec. '75, 7" x 9", $34.95. 
Digital Graphic Display for Oscilloscopes designed by Jim Hogenson and featured in BYTE Oct. '75, 
double-sided card with plated-through holes. $29.95. ^ 

-For CDA 1.1,2.1 - 70-pin wire wrap. Viking NORSMAN w -$5.00. (Postage and packaging per card: $2.00.) 



Our newest line - the COPYDATS, starting at $149.95 FOB Amherst, N.H. 

COPYDAT I - for copies up to 12" x 18" 

COPYDAT II - for copies up to 24" x 36" 

Copies for less than 3i each (Copydat I) - without sacrificing quality. 

Send for a brochure and sample print today! 

CELDflT DESIGN ASSDCIflTES 

BDX 752 AMHERST, N.H. CQCBL 



110 



r 



A COMPLETE 

IK RAM 
SYSTEM 

With CPU card, buffered 
mother card, power supply 
and cabinet. The VERAS 
System is developed 
around the popular F-8 
Series of chips which in 
our estimation is the finest 
and most versatile Micro 
processor now available. 




INTRODUCING THE VERAS F8 COMPUTER 

THE SYSTEM DESIGNED WITH THE USER IN MIND 
THE CPU FEATURES: 

• Two I/O ports on the CPU and ROM chip make 32 bidirectional TTL lines, 

• The Fairbug* programmed storage unit provides the programmer with all I/O subroutines, 
allows the programmer to alter or display memory, and register its contents via teletype. 

• Programmable internal timer is built into the RUM chip. 

• Built in clock generator and power on reset are built into the CPU chip. 

• There is a local interrupt with automatic address vector. 

• It is expandable to 65K bytes of memory. 

• 20 mil loop and/or RS232 interface included. 

• 1K of on board 2102 RAM. 

• Serial interface built into PSU chip. 



OUR 4K RAM BOARD FEATURES: (OPTIONAL) 

• Outputs buffered. 

• On board decoding for any four of 64 pages. 

• Address and data lines are fully buffered. 

• 32 2102-1 static RAM's, 500 ns. or less, requiring no relreshing. 

• No onboard regulators to cause heat problems. 

• 4K memory boards with connector, buffers and static RAM's are available in kit form for $149.00 
The fully buffered mother board will accept (4} 4K RAM boards for a total of 16K bytes of memory. 
Individual power terminals for each 4K RAM board are provided. Memory expansion beyond 16K bytes can 
be accomplished by the addition of more mother boards. Extra buffered mother boards with connector are 
available in kit form for $45.00 
Our regulated power supply is rated at 10 amps ±5V and ±12V, with local regulators which is more than 
adequate to power our basic computer kit and extra RAM boards. 

All boards are high quality G-1 0, double sided, solder plated with gold plated edge connector. 

MECHANICAL FEATURES ARE: 

• AlComplete modular plug in construction. 

• B} Specifically designed rugged aluminum card rack with provisions for voltage regulators (TO -220 

supplied) to keep heat off the boards. 

• C) Designed for convection or optional forced cooling. 

• D) AM I/O ports brought out to the rear panel connectors for easy accessibility. 

• E) Auxilary DC power available at the rear panel to power peripherals. 
Veras Systems is currently developing the following: 

UV PROM board, DMI and DMA board. Cassette, modem, video board and more. All these boards will 
have innovative design, something you will come to expect from VERAS SYSTEMS, 

SPECIAL INTRODUCTORY PRICE FOR THE VERAS F8 

Computer kit is $429.00 or S679.00 assembled. The price will be $459.00 after Sept. 15. 1976. The kit 
includes everything you need to build the VERAS F-8 Computer as described. All boards, connectors, 
switches and discrete components are supplied. Programming manual, data book and support documentation 
supplied. 8K Assembler and Editor (paper tape) available on request with minimum order of 8K RAM. 
Computer dealers and hobbyist club inquires are invited. 
Expocted delivery time 30 days or less. -Fairbug is a registered trademark of Fairchild Corp. 



The More Flexible and Expandible 
I Computer at a Comparative Price. 



VERAS SYSTEMS 



Warranty: 90 days on parts 
and labor for assembled units. 
90 days on parts for kits. 

Prices, specifications and 
delivery subject to change 
without notice. 



> 



l~" 



VERAS SYSTEMS 
A Div. of Solid State Sales, Inc. 
Box 74B, Somerville, MA 02143 
(617) 547-7053 

O Enclosed is check for $ 

or d Master Charge H 



D VERAS F-8 Computer Kit 
□ Assembled 
Include $8.00 to cover postage and handling 

Name 



City, State . 



-Zip. 



INTEL 8080 CPU S29.50 

2518 HEX 32 BIT SR S6.00 

2102-1 1024 ST RAM $ 2.60 

5202A UV PROM $12.50 

MM5203 UV PROM S12.50 

1702A UV PROM S12.50 

5204 -4 K PROM $24.95 

MINIATURE MULTI TURN TRIM POTS 
100. 500, 5K, 10K. 25K. bOK. 100K 200K 

S7Su;n:h 3/S2.00 

MULTI TUHN TRIM POTSSimilai to Bourns 
3010 nyle 3/16"x5/8"x1 J/4"; 50. 100, 
IK. 10K, 50K ohms 

$1.50 tin 3/S4.0Q 

LIGHT ACTIVATED SCR's 

TO-18.200V 1A S 1.75 

TRANSISTOR SPECIALS 

2N3585 NPN Si TO-66 S .95 

2N3772NPN SiTO-3 S 1 .60 

2N4908 PNP Si TO-3 . S 1.00 

2N6055 NPN Si TO-3 Darlington , $ 1.30 

2N5086 PNP Si TO-92 4/5 1 .00 

2N4898 PNP TO-66 $ .60 

2N404 PNP GE TO-5 5/S 1 .00 

2N3919 NPN Si TO-3 RF S 1 .50 

MPSA 13 NPN Si TO-92 3/S 1 .00 

2N3767 NPN Si TO-66 $ .70 

2N2222 NPN Si TO-18 5/$ 1.00 

2N3055 NPN Si TO-3 $ .80 

2N3904 NPN Si TO-92 ....... 5/S 1.00 

2N3906 PNP Si TO-92 5/S 1 .00 

2N5296 NPN Si TO-220 S .50 

2N6109 PNP Si TO 220 S .55 

2N386G NPN Si TO-5 RF S .75 

2N3638 PNP Si TO-5 5/$ 1 .00 

2N6517 NPN TO-92 Si 3/$ 1.00 

C/MOS (DIODE CLAMPED) 

74C02- 25 4016 .40 4035- 1.18 
74C10 .25 401/ 1.10 4042- .68 

4001 .19 4018 1.20 4046- 2.20 

4002 19 4019 .45 4047- 2.20 
4006-1.20 4022-1.00 4049- .43 
4007- .19 4023 19 4050- .43 

4009 .47 4024- .85 4055 - 1.45 

4010 .4 7 4025 .19 4066- .70 

4011 .19 4027- .48 4071- .25 
4012- .19 4028- .85 4077-- .25 
4013 .35 4029- .95 4081- .25 
4015 1.10 4030 .95 4076-1.20 

LED READOUTS 

FND 500-.5" C.C $1.75 

HP 7740-.3" C.C $1 .40 

MAN-4 .25"C.C $1.20 

MAN 7 .3" C.A SI .25 

NS 33-3 rliii. array S1 .35 

25t lor out catalog (ealurini 
ranslstors and Rectifiers 
mpshireSt,, Cambridge, Ma; 



PRINTED CIRCUIT BOARD 



4-1/2"x6 1/2"SINGLE SIDED EPOXY 
BOARD 1/16" thick, unetched 

$.50 en 5/S2.20 

VECTOR BOARD 1" SPACING 

4.5" x 6*' SHEET SI .50 



4 WATT IR LASER DIODE $7.95 



2N 5460 P FET S .45 

2N 5457 N FET $ 45 

2N 4891 UJT $ .45 

TIS 43 UJT S .35 

ER900 TRIGGER DIODES 4/S1.00 

2N6028 PROG. UJT $ .65 

VERIPAX PC BOARD 
This board is u 1/1 6" Single sided papei epoxy 
board. 4V/'x6V DRILLED and ETCHED 
which will hold up to 21 single 14 pin IC's 
or 8, 16, or LSI DIP IC's with bussas for 
power supply connccioi . . $4.00 







MT-2 PHOTO TRANS 
RED, YELLOW, GREEN OR 

AMBER LARGE LED's 
14 PIN DIP SOCKETS .... 
16 PIN DIP SOCKETS .... 


.... $ .60 

.... $ .35 
$ 35 


8 PIN MINI DIP SOCKETS . 


1000/S8.00 
. . . .$ .30 


10 WATT ZENERS 3.9, 4.7. 




1 WATT 2ENERS 4.7, 5.6. 10, 
18 OR 22V . . 


12. 15. 



Silicon Power Rectifiers 



SILICON SOLAR CELLS 

2Vt" diameter 
5V at 500 ma $5.00 ea., 6/S27.50 



REGULATED MODULAR 
POWER SUPPLIES 

*- 15 VDC AT lOOma 

115VAC INPUT . . . 
5 VDC AT 1 A. 11SVAC INPUT . . . $24.95 
12 VDC AT .54 $24.95 



TANTULUM CAPACITORS 



.22UF 35V 5/S1.00 6.8UF 35V 3/51.00 

.47UF 3GV 5/S1.00 33UF 25V $.40 

.68UF 35V 5/S1.00 30UF 6V 5/S1 .00 

1UF35V 5/S1.00 150UF20V $.50 
1.7UF 3GV 4/S1. 



CT7001 ALARM CLOCK CHIP . 



J-,'.7!i 



NATIONAL MOS DEVICES 

MM1402 3.20 MM50B7 4.00 

MM14Q3-3.20 MM5058 4.95 

MM1404-2.50 MM5060 -4.95 

MM5013 7.75 MM5061 4.30 

MM 50 16 3.50 MM5555- 6.25 

MM5017-4.75 MM56S6 6.25 

MM5055 -4.00 MM5210 1.95 

MM5056 4.00 MM5260 2.95 



PRV 


1A 


3A 12A 


BOA 


125A 


100 

200 
400 


.06 
.07 

.09 


.14 .30 
.20 .35 

.25 .50 


.80 

1.15 
1.40 


3.70 

4.25 
6.50 


600 


11 


.30 .70 


1.80 


8.50 


800 


.15 


.35 .90 


2.30 


10.50 


1000 


20 


.45 1.10 


2.75 


12.50 



74 LOO 
7400- 
7401- 
7402 
7403- 
7404- 
7405- 
7406- 
7407- 
7408- 
7409- 
7410- 
7411- 
7412- 
7413- 
7414- 
7416- 
7417- 
7420- 
7426- 
7427- 
7430- 
7432- 
7437- 
7438- 
7440- 
7441- 



LIC SERIES 






7442 




74126- 


.48 


7445 


.79 


74150- 


1.0U 








.64 






74153 


.69 






74154 


1.0b 








.79 






74157- 


,6b 








,yy 








I.Ub 






74165 


1.0b 




.42 


74173 


1.30 






74174 


1.00 




.95 


74175 


.90 




.33 








2.00 


74180 


.n 




,47 


74181 


2.1 




.69 


74190- 






.47 


74191 


1.10 


7493 




74192 




.76 


74193 


1.00 




.70 


74194 






.73 


74195 






.30 


74196 






.37 


74283- 


1.b0 




.65 


75324- 






.49 


75491 - 








7549? 





MINIATURE DIP 


SWITCHES 




CTS-206-4 


Four SPST 


witches 






In one 


ninidip pack 


K|C. 


$1.50 


CTS. 206-8 


Eight SPST 


swiiclies 


n .i 


16 


pin uii 


package 




S2 


bb 



Full Wave Bridges 



SANKEN AUDIO POWER AMPS 

Si 1 01 G 1 WATTS $ 6.90 

Si 1020 G 20 WATTS SI 3.95 

Si 1050 G 50 WATTS S24.95 

PRV 2A ~ " _ 6A~ ~ 25A~ 

200 .95 1. 25 2.00 

400" .. . M S . ._, 1-50 _ 3 00 

600 " 1.3b 1.75 ' 4.00 
CD 1 10 LINEAR 256 XI BIT S"ELF 
SCANNING CHARGED COUPLED 

D EVISE S99.00 

LINEAR CIRCUITS 

LM309K 5V 1A REGULATOR . . . S1.00 

723 - 40 i 40VV REGULATOR $ .80 

301 '748-Hi Per. Op. Amp S .28 

320Tb. 12, 15, OR 24V 

NEGATIVE REG $1.35 

741 A or 741 C OP AMP S .28 

710 COMPARATOR S .32 

307 OP AMP $ .25 

CA 3047 Hi Pel Op. Amp S .95 

340T5, 6, 8, 12, 15, 18.24V POS 

REG. TO-220 $1.20 

101 OPER. AMP. HI PERFORM. . . , $ .75 
LM 308 Opar. Amp., Low Power . . -SI .05 

747 -- DUAL 741 S .65 

556 - DUAL TIMER . . _ S .95 

537 - PRECISION OP. AMP SI. 70 

540-70W POWER DRIVE S2.7b 

LM3900 OUADOP. AMP S 49 

LM 324 - OUAD 741 $1.05 

b60 - PHASE LOCK LOOP $2.00 

561 - PHASE LOCK LOOP $2.00 

565 - PHASE LOCK LOOP SI. 50 

566 FUNCTION GEN SI 65 

567 - TONE DECODER $1 75 

LM 1310N FM STEREO DEMOD. . . $2. 7b 
8038 IC VOLTAGE CONT. OSC. . . $3.90 
LM370 - AGC SQUELCH AMP. , . SI. 15 

bb5 - 2jis - 2 HR. TIMER S .47 

bb3 OUAD TIMER $2.50 

FCD 810 OPTO-ISOLATOR S .80 

1488 DUAL OP AMP S .5b 

LM 380 - 2W AUDIO AMP $ .9b 

LM 377 - 2W Stereo Audio Amp. . . S2.b0 

LM 381 - STEREO PREAMP SI .25 

LM 382 - DUAL AUDIO PREAMP . S1 .25 
LM 311 - HI PER. COMPARATOR . S ,9b 
LM 319 - Dual Hi Speed Camp. . . . $1.10 
LM339 - OUAD COMPARATOR .$1.15 



some cases, but it can be done with any 
processor including the 8080. 

I think that the real advantage here lies 
with the 8080 for it can address 10 as 
memory and also address 10 via its IN/OUT 
commands and not limit the memory 
address by using them for 10. The 6800 does 
have advantages. It has two accumulators 
which simplifies some programs, but unfor- 
tunately it has no additional user registers on 
the chip, its interrupt system also is an 
advantage. 

Each of these systems have advantages 
and disadvantages and each user must deter- 
mine which suits his need best. The one 
criteria that needs to be considered before 
choosing a processor for non-professional 
use is the software available for it, and the 
cost of this software. I feel that for this 
market the choice must almost be made 
solely on the basis of the software. 

John W Cochran 

820 Orwell Av 

Orlando FL 32809 

ACHTUNG! 

If there's one thing a home computerist 
enjoys more than his "calculatin engine," it's 
showing off his pride and joy to his girl- 
friend, neighbor, or some unsuspecting 
stranger who happens by his front door. 
Nothing, however, can ruin this joyous 
occasion more than having a curious on- 
looker flip the wrong switch and successfully 
erase your favorite version of Star Trek that 
you just spent so long setting up for a 
demonstration. In order to keep these situ- 
ations to a minimum, I offer the following 
announcement which I have attached to my 
Altair 8800. 

ACHTUNG! 

DAS MACHINE 1ST NICHT FUR 
GERFINGERPOKEN UND MITTEN- 
GRABEN. IS EASY SCHNAPPEN 
DER SPRINGENWERK, BLOWEN- 
FUSEN UND POPENCORKEN MIT 
SPITZERNSPARKEN. 1ST NICHT 
FER GEWERKEN BY DAS DUMM- 
KOPFEN. DAS RUBBER-NECKEN 
SIGHTSEEREN KEEPEN HANDS IN 
DAS POCKETS UND WATCH DAS 
BLINKENLIGHTS. 

Glen Brickey Jr 

3166 Santiago Dr 

Florissant MO 63033 

This little frivolity is derived by the 
omission of one word from an earlier version 
which has graced amateur radio shacks and 



laboratories for several decades . . . it's just 
as applicable to computer rooms. 

MORE ARTICLES FOR HOUSEWIVES 
NEEDED 

As a computer hobbit's wife who just 
completed the Evelyn Woods course [in 
speed reading] and accomplished exactly 
what the advertisement states [namely, read- 
ing JAWS in 56 minutes], I was really 
disappointed in the April issue of BYTE. 

It took me exactly 12 minutes to read all 
96 pages. Come on, guys, how about a few 
hundred more pages for us housewifes? 

Dorothy Dundon 
Bolton MA 

PS: Fortunately, the course doesn't guar- 
antee that you'll understand what you are 
reading. 

HERE'S WHAT I'D LIKE TO SEE 

I have been very pleased with your 
magazine and am glad I subscribed. I have 
some suggestions for articles I would like to 
see. I would like some articles on bit slice 
micros, and the electronic considerations of 
building your own system from scratch such 
as power supplies, bus terminations, etc. 

Also I would like to see some articles on 
how to write routines for floating point 
conversion, arithmetic and scientific func- 
tions such as. sine, log, etc. 

This information would be very helpful 
for those of us who want to design and build 
our own hardware and software systems. 
Keep up the good work. 

Mark Mickelsen 
Draper UT 

Potential authors, take note. 



GAMES AREN'T FAIR GAME! 

Paul Kanciruk in a letter printed in the 
February 1976 BYTE states that he would 
like to see less software on games and that 
many do not want to play "super space 
electronic hangman life-war pong." 

I believe that Mr Kanciruk has missed the 
point of games completely. Indeed, many do 
not want to play every game that they see in 
print, and certainly I don't either, but I do 
read them all, as a rule. 

A game program serves as a common 
ground for passing along programming tech- 
niques. Paul Kanciruk uses computers for 
statistical analysis. Fine. Except, if he 
wanted to show me a clever programming 
trick, I doubt if I could appreciate it, or even 



112 



World's Lowest 
IC Prices 



TTL 






LOW POWER SCHOTTKY 




7400 14 


74151 


60 


74LS00 


25 


74LS164 


1 50 


7402 14 


74157 


60 


74LS02 


25 


74LS174 


1.50 


7404 16 


74160 


75 


74LS10 


25 


74LS175 


1 50 


7410 14 


74161 


75 . 


74LS73 


40 


74LS193 


1.50 


7420 14 


74163 


75 


74LS75 


50 


74LS251 


1.50 


7427 25 


74165 


80 


74LS151 


85 


74LS253 


1.50 


7438 25 


74173 


1 25 


74LS153 


95 


74LS257 


1.50 


7440 14 


74174 


75 


74LS157 1 


50 


74LS258 


1 50 


7445 45 


74175 


75 


74LS163 1 


50 






7447 65 


74177 


70 


CMOS 






7450 14 


74180 


80 


4001 


16 


4027 


40 


7451 14 


74181 


1 50 


4002 


16 


4028 


60 


7473 22 


74191 


1 00 


4006 


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113 



understand it. The reason: I don't know 
anything about statistical analysis. 

The same holds true for an astronomer 
showing a program to a marine biologist. 
There is no real way one can visualize how 
clever or intricate some technique can be if 
the problem is not understood. 

On the other hand, everyone can under- 
stand Pong or Life or some other game. In 
them, every programming trick can be 
covered. Anyone reading the program can 
see what does what, because what is lo be 
accomplished can be understood. 

It's not so much a matter of wanting to 
play games or not, but a matter of learning. 
Next time, when Mr Kanciruk sees a game, 
maybe he will read through it this time. He 
may find it pretty enlightening. 

Craig A Pearce 
Berwyn IL 



A LITTLE PLUG FOR ACM 

Understand that you can always use some 
copy. Tell you what - here's a little plug: 

The Association for Computing Machin- 
ery has been the major society for com- 
puting professionals. For better than 25 



years, the ACM has published papers of 
interest, held annual conferences and aided 
the advancement of computer science. Most 
of the real work of the Association is done 
in its local chapters and special interest 
groups. The local chapters are located 
throughout the nation, and provide a forum 
for interested people. They also bring in 
speakers of prominence on many topics. 
Although there are many special interest 
groups, the one that may be of most interest 
is the Special Interest Group on Mini- 
computers (SIGMINI). This group is 
interested in mini- and microcomputers, 
their hardware, software and firmware. They 
are also interested in problems and experi- 
ences pertaining to the use of small systems. 
They publish a bimonthly newsletter that is 
always of interest. One need not be a 
member of the ACM to join SIGMINI. Dues 
are only $7 per year — a very reasonable 
price. 

SIGMINI's address is: 

ACM -SIGMINI 

PO Box 12105 

Church St Station 

New York NY 10249 

I have been interested in computing on 
the smaller and less formidable levels for 



At Last! 

BYTE T-shirts are here! 




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medium 

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Other colors, styles I'd like to see_ 



114 



MC14412 UNIVERSAL MODEM CHIP 
MC14412 contains a complete FSK modulator and de-mod- 
ulator compatible with foreign and USA communications. 
(0-600 BPS) 
FEATURES: 

.On chip crystal oscillator 

.Echo suppressor disable tone generator 

.Originate and answer modes 

.Simplex, half-duplex, and full duplex operation 

.On chip sine wave 

.Modem self test mode 

.Selectable data rates: 0-200 

0-300 
0-600 
.Single supply 
VDD=4.75 to 15VDC - FL suffix 
VDD=4. 75 to 6 VDC - VL suffix 
TYPICAL APPLICATIONS: 

.Stand alone - low speed modems 
.Built - in low speed modems 
.Remote terminals, accoustic couplers 

MC14412FL $28,99 

MC1441 2VL $21 .74 

6 pages of data .60 

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MC14411 BIT RATE GENERATOR. 
Single chip for generating selectable frequencies for equip- 
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rates which are multiplied under external control to IX, 
8X, 16X or 64X initial value. Operates from single +5 

volt supply. MC14411 $11.98 

4 pages of data 40 

Crystal for the above $4.95 



7 WATT AUDIO AMP Fairchild TBA 810S Monolithic 
I.C. Class B audio Amp works over wide range of power 
supply voltages. 1 watt at 6V, 7 watts at 16V. 

TBA - 810S $ 2 - 75 

Data for the above 60 



4 DIGIT COUNTER. MM74C926 is a 4 digit counter with 
7 segment output. Carry output for cascading and intermal 
display select allows outputting of counter or set of 
internal latches. 3 to 6V operation. Great for clocks, 
event and frequency counters. 
MM74C926- with spec sheet SI 2.00 



FOUR QUADRANT MULTIPLIER. MC1495L provides 
output as a linear product of two analog input. Use 
for frequency doubler, balanced modutar/demodulator, 
electronics gains control. 

MC1495 L $5.50 

6 pages of specs 60 

9 pages of applications 90 



TELETYPE CODE CONVERSION CHIP 

MM5220BL converts 5 level Baudot into 8 level ASCII. Use 

this chip to make your old TTY talk to your new computer. 

MM5220BL $1 8. 00 

Specs for the above .30 



MOS TIME BASE KIT, 

Only 1" X 1.5". Input 5 to 15 VDC, output is 60HZ 
square wave for portable or mobile clocks. PC board is 
drilled! MTBK-60HZ $5.88 




78H05 Voltage regulator. Fairchild 5V, 5A, TO-3 reg- 
ulator. Take care of those heavy current requirments with- 
out separate regulator/pass transistor combinations. Use it 
with the same ease of instalation as the 309K(same pin 
arrangement.) with specs $11 .25. 



-T- 



LM317 Voltage Regulator. 1 .5A, 3 terminal adjustable 
regulator in TO-3 case. Adjusts from +1.2V to +37V. 
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,01%/V line regulation. No need to stock assorted reg- 
ulators - just stock resistors $4.99 

Specs for the above 70 

DATA BOOKS BY NATIONAL SEMICONDUCTOR 

DIGITAL. Covers TTL, DTL, Tri-State, etc $3.95 

LIN EAR, Covers amplifiers, pre-amps, op-amps, . . $3.95 
LINEAR APPLICATIONS. Dozens of application notes and 
technical briefs covering the use of op-amps, regulators, 

phase locked loops and audio amps $3.25 

CMOS Gates, Flip Flops, registers, functional blocks $3 
VOLTAGE REGULATORS. A must for anyone making a 
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MEMORY. Information on MOS and Bipolar memories': 

RAMS, ROMS, PROMS and decoders/encoders $3.95 

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display driver and opto-couplers $3.95 

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DATA BOOKS FROM FAIRCHILD. 

uA Linear. 776 pages of data and applications for Fair- 
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CA301 A. .Improved, general purpose op-amp, 8 pin dip.. 59$ 

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CD4059 IS BACK ■ Now, again in stock is the 
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CD 4059 AE $6.50 

Specs for the above 50 

DC to DC CONVERTER MODULE. Tiny potted module is 
a complete regulated output up-converter. 4.5V D. C. 
input provides approximately 14V @ 12 mA. Will operate 
down to 2.5V with reduced output. Size only 1 " X £" X {" . 
With connection diagram $1 . 25 



NSL4944 LED. Current regulated, universal diffused-lens 
red LED lamp. A GaAsP solid-state high intensity LED 
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No series resistor needed. Typical 13mA forward current, 
NSL4944 with panel mounting clip 89$ 



D-A CONVERTER BY ZELTEX 

8 bit precision hybrid circuit for use in controllers, timers, 
volt meters, etc. Molded plastic package with P.C. pins. 
Super buy on this better than usual subsystem. ZELTEX 
model ZD430. DAC-430 $4 .95 



NEW BOOK!!! "An Introduction to Microcomputers" 
This is the book which Fairchild Semiconductor Company 

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view of real microcomputers. IMC-001 $8.00 



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some years. My first experience came wherl I 
was introduced to the PDP-11 that Portland 
State University bought. I found it hard to 
believe that such computing power came in a 
desktop package. Since then I have started a 
minicomputer interest group in Portland, 
worked with an Interdata mini system, and 
joined the SIGMINI. I really feel that there 
will be many systems going in at this level in 
the future. IBM has even endorsed (blessed?) 
the concept with its 5100. 

In conclusion, I feel that you at BYTE 
are doing a good job in an area that hasn't 
been touched by the biggies. Lots of luck. 

Percy G Wood 
Woodburn OR 



SOME WIRE WRAP POINTERS 

I would like to compliment you on your 
article on wirewrapping in the January issue. 
Based on considerable experience in the Bell 
system's new switcher, I offer the following 
items: 

1. Wire Strippers: Nicked wire, especially 
when it's 30 gauge, will usually break 
when a wrap is attempted. The only 
consistent, reliable strippers I have 
found are made by the Clauss Cutlery 
Co, Freemont OH. They are sold 
under the NO-NIK trade name. While 



3. Wire Slack (or more specifically, lack 
of it): Interesting thing about running 
a wire making a 90° bend around a 
square, sharp wrap pin, is that suffi- 
cient tension with time causes the in- 
sulation to part, allowing an uninten- 
tional connection (short). Heat or 
vibration will accelerate the process. 
The problem is sometimes called cold 
flow, cut thru, and several unmention- 
able names. Sometimes this problem 
will manifest itself as a trouble which 
disappears as soon as you touch the 
wiring. The best cure for this problem 
is when you wrap, be sure there's a 
little slack in the wire after both ends 
are wrapped. The time and money it 
costs you is cheaper in the long run, 
unless you like spending time to find 
this problem and money to replace the 
chip(s) the cold flow destroyed. 

4. Color Coding: If you can get colored 
wire, use several colors. It makes 
debugging and later modifications 
much easier. 

Alan Andrews 
Chicago IL 

NO-NIK wire strippers are the only ones 
I ever use . . . CH 




not cheap (about $14), they have 
worked for me, every time. Inasmuch 
as they are precision, one pair is 
needed for 30 gauge, and another for 
28 gauge. Maybe one of BYTE's 
advertisers will pick up on them. 
Presently they are only available 
through distributors. 
2. Tweezers: A good pair of fine point 
tweezers are very good for picking out 
snivels and broken pieces after an 
unwrap operation. The alternative of 
leaving wire pieces in a back plane 
usually results in a good application of 
Murphy's Law at worst, and some very 
frustrating intermittent problems at 
best. I hate to tell you how many 
hours have been spent digging wire 
pieces and snivels out of backplanes, 
which seemed to fix "impossible" 
problems. 



COMMENTS ON THE 
INFORMATION REVOLUTION 

I've been in large scale digital computer 
maintenance for eight years and am now 
with my second computer company. In that 
electronics and computers put bread and 
butter on the table, it's my belief I have a 
responsibility to be aware of the history, 
technology and future of my chosen profes- 
sion. Textbooks and organizational literature 
are a great place to start, but to stay abreast 
of the times one must turn to current 
periodicals. Electronics in general is amply 
represented by many fine publications, but 
until recently the best computer literature in 
these lines was aimed at computer software 
and management. Why the gap for computer 
hardware and experimenters? Simple; they 
were locked away in laboratories of major 
companies, and engineering journals suf- 
ficed. Outside, in the general market, cost 
prohibited all but cursory investigations into 
computer applications. 

After reading the January 1975 Popular 
Electronics article on the ALTAI R 8800, I 
was struck with a thought — this was the 
beginning of a revolution not only in com- 
puter technology but in something larger by 
far. A few years back I came upon a book by 



116 



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CD4017 
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TD4029 
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CMOS 

C04035 1 85 

CU4040 2 45 

CD4D4? I 90 

CD4044 1 50 

CD4046 2 51 

CU4047 2 75 

C04049 79 

CD4050 79 

CD405I 2 95 

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CD4060 3 25 

C04066 1.75 

CD4069 4S 

CO4071 45 

CD4072* 45 

CD40S1 45 

CD4511 2 

CD4518 2 

74 COON 39 

74C02N 55 



74C04N 

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MC74 

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74C107N 

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74C154 

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74CI64 

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74C195 

MC4044* 

MCI 40 16* 



LM30QH 

IM301H 

I \13QlCN. 

LM302H 

IM304H 

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LM308M 

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LM309H 

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LM320K.1? 

LBHfJK 15 

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IM340K-15 

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IM340T-5 

IM340I 6 

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IM370N 

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LINEAR 



LM377N 

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HE501K 

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XA-320P 


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DATA HANDBOOKS 

7400 Pin-cut & Descriplion ot 5400/7400 ICS S2.95 

CMOS Pin-out & Description ot 4000 Series ICS $2.95 

LINEAR Pm-oul & Functional Description $2.95 

ALL THREE HANDBOOKS $6.95 



CONSUMER ELECTRONICS 



exelar 




DIGITAL WATCH 

This walcn is manulactLiied 
Dy National Semiconducloi 
It provides 5 functions, 
fiours. minutes, seconds, 
dale. AM indicator dot 
Accuracy is assured to 5 
"seconds per month Dy pre- 
cision Quam crystal I' 
something should go wrong 
with the watch, repair is as- ' 
sured within 48 hours afler it 
is received Complete with 
si eel black leather band 

ES4-YS 

3 MICRON GOLD 
PLATE BEZEL 

$29.95 

NOT A KIT 



Hovus 




DIGITAL ALARM CLOCK 

This 4 dicit Novus Alarm Clock is a very reliable and smaily 
styled unil 11 provides such features as an alarm sellable to any 
minule ol ihe day, a 7 minutes snooze alarm, a power faiLre 
indicator, and even an A.M.. P.M indicator. 



NOT A KIT 



$19.95 



xciton OPTO ELECTRONICS 

LITRONIX DISCRETE LEDS 

MONSANTO 



125' 


dia. 


XC2Q9R 
XC209G 
XC209Y 
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SSI 

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4/$1 

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mi — 

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dia. 


XC22R 
XC22G 
XC22Y 
XC220 


SSI 

4S' 

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Each assortment contains 14 pes ol 10 li 



II pots are available in single umi guanines S.9 



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Robert M Hayes and Joseph Becker, pub- 
lishers and authors in their own right and 
now associated with John Wiley and Sons, 
Inc. They presented a concept I have held to 
since first reading. Their book was part of a 
series, which in their words ". . . is designed 
to include books that are concerned with 
various aspects of communicating, utilizing, 
and storing digital and graphic information. 
It will embrace a broad spectrum of topics, 
such as information system theory and 
design, man-machine relationships, language 
data processing, artificial intelligence, 
mechanization of library processes, non- 
numerical applications of digital computers, 
storage and retrieval, automatic publishing, 
command and control, information display, 
and so on." Their reason for the series I 
considered most important. "Information is 
the essential ingredient in decision making. 
The need for improved information systems 
in recent years has been made critical by the 
steady growth in size and complexity of 
organizations and data. Information science 
may someday be a profession in its own 
right." 

This was the answer to a question I didn't 
know how to phrase. Computers are not the 
desired end; they are but tools used in 



working toward an end. Manipulation of 
data is not the goal, but availability of data 
for use. Developing control systems is not 
our prime function, but freeing ourselves 
from the task of controlling so we can 
advance toward our selected end is. Com- 
puter science is a technology that is a part of 
the larger field of data processing. DP in turn 
resides as a part of this thing called Infor- 
mation Science. 

What has this got to do with BYTE and 
an ALTAI R 8800? Progress is retarded when 
ideas and technology are cloaked within 
institutions and discussed in esoteric terms. 
Progress isn't made with black boxes and 
magic. Progress begins with understanding, 
understanding the problem, the desired ends, 
and the tools at hand. With the advent of the 
"affordable" computer, people from many 
disciplines, backgrounds, experience and 
with many problems and solutions, are 
getting into data processing. It will be this 
broad background of "scientists" that will 
produce new, innovative, and productive 
directions to Information Science. Similari- 
ties may be drawn from mechanics, Watt and 
the steam engine, electronics, Baird (no 
relation to the writer) and television, arma- 
ments, Williams and the carbine. True, insti- 




Computing 1776 Poster 



Robert Tinney painted a beautiful oil painting on a bicentennial 
theme bridging two centuries of America's development. This 
painting has been reproduced on the cover of this issue, and a 
full-sized poster in color without the BYTE logo has been 
printed for you. It will make a perfect wall decoration in your 
office, home or computer room. 

The poster is 20" by 24" (51 cm by 61 cm) large with a white 
border of 2 inches (5 cm) at all four sides. The image size is 16" 
by 20" (41 cm by 51 cm), and it is the original size. The price is 
$2.95 postpaid, and the poster is shipped in a mailing tube to 
avoid folding. Only 2,000 copies have been printed on the first 
run wtiich will be sold on a first come first served basis. So hurry 
if you want to be among the first to show this beautiful poster 
to your friends. 



BYTE Posters 

PO Box 274 

Jaffrey Center NH 03454 

603-924-7217 

Name 



Allow 6-8 weeks for processing. 



Posters $2.95 each 



Address . 



City. 



-State . 



-Zip- 



□ Bill BankAmericard 

□ Bill Master Charge 
No 



□ Check Enclosed 
$ 



. Exp. Date . 



118 



S. D. SALES CO. 



P. O. BOX 28810 
DALLAS, TEXAS 75228 



UP YOUR 
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new 21L02— 1 low power and super fast RAM's. 
Allows you to STRETCH your power supply 
farther and at the same time keep the WAIT 
light off. 

8 for $17.50 



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with keytops. For encoders, combination locks, etc. 




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Please call between 8:30 AM and 6:00 PM C.S.T. - Monday 
through Friday. You may also call to check stock or just ask a 
question. However, only B.A.C. and M.C. orders will be accepted. 
We do not ship C.O.D. (See terms of sale on other page.) 



tuitions do make dramatic advances. They 
are not the evil creatures many would 
believe them to be; but an involved, inter- 
ested general public can work wonders to 
dwarf the efforts of our mightiest con- 
glomerates. 

However, let us pause before we plunge 
headlong into our new race for advancement 
and consider the problem of rediscovering 
the wheel. For example, the German printer 
Gutenberg invented the printing press with 
moveable type. This was unfortunate, be- 
cause this "invention" had been in use since 
well before Gutenberg was born. That this 
man, with his skill and ambition, was re- 
moved from information on the advance of 
other societies is understandable due to the 
lack of communication between societies. For 
the ambitious craftsman of today to suffer 
the same situation because of a lack of 
communications among individuals is a 
travesty. The answer to this problem is easier 
stated than the problem. COMMUNICATE. 
How? Through the media. Which? Publica- 
tions — and thus we arrive, delightfully, at 
BYTE. 

BYTE must be, and so far has been, a link 
that provides for information, education, 
discussion, development and debate. A two 
way link between the editor, authors and 
companies and an increasing rank and file of 
the informed and to-be-informed informa- 
tion-using public. BYTE is in the forefront 
of this revolution in computers, data proc- 
essing and information science. If you and I 
choose not to face our responsibilities in 
making the communications aspects of 
BYTE work, we only hinder the dawn of a 
new age of discovery. If, however, we 
involve ourselves in making the media work 
to its designed ends, BYTE, those associated 
with it, and the information society will 
benefit from our efforts. 

Thanks for your time. Keep up the good 
work. Your efforts with BYTE so far are 
deeply appreciated. 

John T Baird 

Sperry Univac 

Okinawa JAPAN 

SOME IDEAS 

I was one of those who were intrigued 
enough by your prospectus to see what your 
magazine would be like, and I am pleased. I 
have learned a great deal about computers 
from your pages, enough that I want to have 
a system of my own to play with. BYTE is 
described by some as being "hardware 
oriented" and that's not bad; but it seems 
that most of its articles assume considerable 
knowledge of computers, leaving the 



interested-but-ignorant scrabbling around 
wondering where to start to learn. I have 
questions like these: 

How difficult would it be to get a 
simple 8008 based system going from 
"scratch" (buying chips and parts and 
going from there)? 

What kind of test equipment would I 
need? An oscilloscope? How good? 

Has anyone ever published the sche- 
matic for such a system? With tips and 
pitfalls? 

Has anyone ever described how to 
order PROMs programmed with basic 
programs such as loading, monitoring 
and debugging routines? Are these 
copyrighted? How about assemblers? 

I have noticed that you have been run- 
ning articles for the uninitiated. Keep it up, 
and remember that there are some of us out 
here who need explanations at a very basic 
level. Also please get review articles about 
kits published as soon as possible after 
introduction. Those who go this route will 
need to be aware of what they are getting 
into. 

Thanks for the good work. 

Robert H Irwin 
Berkeley CA 

HARD UP FOR HARD COPY? 

One of the major problems encountered 
in building one's own computer — either 
from scratch or from a kit — is the 10 
situation. I think it's fair to say that if you 
want hard copy, it's going to cost you about 
a thousand bucks. This problem has been 
mentioned by several of the authors in your 
magazine, but none of them has suggested 
the obvious remedy. 

There must be tens of thousands of five 
level teleprinters floating about in the US 
and Canada. Unlike the Model 33 most of 
them were built to last, and they can give 
many more years of reliable service. Their 
most important qualification is their cost. 
They can be had for less than $ 100 for the 
most part. This particular machine that I am 
using to type this letter had less than 300 
hours on it and cost me $25. 

It may appear to be a backward step to 
go to the Baudot code and they are some- 
what slower than the Model 33s, but they 
are just about the only game in town. Even a 
TV typewriter of some sort will end up 
costing about $500 and you still haven't 
solved the problem of hard copy. 

I feel that if some microprocessor kit 
maker offered a PROM monitor and an 



120 






-4 



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use 7473 I.C. 
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3 Octaves Full Size 

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MEMORIES 

1702A Erasable Prom S13.50ea. 

2102 1 1024 BIT Static RAM $2.25 ea. 
Over 10 pes. $1.99 ea. 




Too* 



2107A4K RAM 
in 22 pin DIP 
4096 BIT Dynamic Memory, Intel 
Prime Units 

$16.50 each or 4 lor $60.00 
TTL AND CMOS PRICE LIST WILL BE 
MAILED OUT ON REQUEST. 



COMPUTER GRADE 
CAPACITOR 

15500 MFD 
75 V DC 
S4.95ea 

5600 MFD 
60V DC 
SI. 25 fa. 



SAE DIP SWITCHES 



^^frr ; 



► 
► 



4 Toqi|leSPST Switches on a Mini DIP 

18 pinsl Only SI. 50 ea 
8 Toggle SPST 5-v.iches on a DIP 
( 1 6 pins) Only S2.60 e.i 

SUBMINIATURES TOCCLE 
SWITCHES 



A A 



SPDT On None-On $t.30e< 
DPDT On None-On S1.50e; 



m 

EECO BCD THUMBWHEEL 
SWITCHES 

8 positions SI .25 ea. 

10 positions $2.15 ea. 

'JIA 12 positions S2.50ea. 




QUARTZ CRYSTALS 

1 MHZ Computer Crystals S4 25 ea 
3 58 MHZ Color TV 
Crystals SI .25 ea. 

Use with Nation MM 5369 lo make 
;i fieilect nnie base for clock. 




NATIONAL MM 5369 17 
STAGE PROGRAMMABLE 
OSC/DIVIDER generate A 
60 H/ reference Frequency 
with a 3-58 MHZ Color TV 
XTAL in Mini DIP Package 

ONLY S2.25 each 



NEW ALARM CLOCK CHIPS 



ONLY $3.50 ea. 




Da 


a .261 


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PRUDRAMMAIUf. OPTIONS 


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Aljrm Counlti 
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MINIMUM ORDER $10.00. California residents add 6% sales and 1 .50 to cover postage and handling. 
Out-of-state and overseas countries add $2.50. 
.<ff>. SEND CHECK OR MONEY ORDER TO: 

i § FORMULA INTERNATIONAL INC. 

YmYmVC* 12603 CRENSHAW BOULEVARD • HAWTHORNE, CAL.I FORNI A 90250 ^. 

** For more information please call 12131 679-5162 p> 

STORE HOURS 10-7 Monday - Saturday 8/76 p» 

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY 



interface for these machines, he would be 
doing the hobby a great service. 

Finally, I would like to commend you on 
the fine magazine. I personally would like to 
see more detailed construction articles and 
more emphasis on hardware but have found 
the present mix pretty good. 

J A Koehler 
Saskatoon, Saskatchewan 

Mr Koehler 's letter was sent to BYTE on 
pin feed paper with excellent copy. The 
following is a reduced sample from the 
letter 's original copy: 



THERE MUST BE TENS OF THOUSANDS OF FIVE LEVEL TELEPRINTERS 
FLOATING ABOUT IN THE U.S. AND CANADA. UNLIKE THE MODEL 55 MOST OF 

THEM were built to last and they can give many more years of 

RELIABLE SERVICE. THEIR MOST IMPORTANT QUALIFICATION IS THEIR COST 
THEY can be had for less than ioo DOLLARS FOR The MOST PART. THIS 

PARTICULAR MACHINE THAT I AM USINC TO TYPE THIS LETTER HAO LESS 
THAN 500 HOURS ON IT AND COST ME 25 DOLLARS. 



GOTCHA 

Dear Nameless BYTE Employee: 

Enclosed is a check for $12 for a year's 
subscription to BYTE magazine. I got tired 
of stealing others' issues and copying them 
at the office. 

Thomas J Kaminski 
Greenbelt MD 

PS: Excuse my writing. My hand is in a cast 
after some wretched BYTE issue No. 1 
owner caught me reaching into her desk 
drawer for the copy. 

There are no nameless B YTE employees. 
The staff section of the contents page names 
every person who is connected with the 
magazine. 



INSURMOUNTABLE? 

Everyone has problems. Mine are insur- 
mountable. After sitting around for a 
month, snapping at every creature and/or 
machine that has crossed my path, I have 
discovered the prime cause of my difficul- 
ties: I haven't seen an issue of BYTE since 
Christmas. Since I am a Navy officer sta- 
tioned in Guam, I could not find a copy to 
mooch (or steal, etc). Maybe I am the only 
subscriber on Guam? 

Second class mail (for me) goes from New 
Hampshire to the FPO in San Francisco. 
After the FPO reads my BYTE, they (must) 
send it to their friends at the post office in 
Hawaii. Maybe someone there has a friend in 
Midway? It seems as if the issue(s) enroute 
are passed through (and read by) every post 
office between us. They have high mileage 
when I get them. 

Anyway, is it possible to have my very 
own personal copy of BYTE sent by first 
class mail? This will reduce the month and a 
half handling (reading) period and maybe 
encourage those in the FPO, Hawaii, etc, to 
purchase their own personal copies since it is 
hard to read all of each issue when they go 
through as fast (?) as first class. 

Thomas D Dean 
FPO San Francisco CA 

Here's mud in our eye (for now). Com- 
puter programs don 't spring forth by magic, 
even for computer magazines. Many people 
have asked for the privilege of paying extra 
postage and getting B YTE by first class mail 
or AO book rate air mail overseas. We have 
not yet implemented any features in BYTE's 
circulation management system to handle 
special cases. When and if such provisions are 
available at a future date, we'll put a note 
into the magazine. 



What's 

New? 



A First Briefcase Computer? 

A new company, STM Systems of Mont 
Vernon NH, has come out with a unique self 
contained computer system which is shipped 
in a briefcase and requires only a standard 
television monitor and audio cassette 
recorder to serve as peripherals. The BABY! 
computer is a complete 8 bit system with an 
MOS Technology 6502 processor, 2 K of 
programmable memory, an ROM monitor, 
video display generator, audio cassette inter- 
face, keyboard and power supply and 
attache case. The computer itself is the 
lucite plastic case sitting inside the attache 
case in photo 1. It measures 14.5 inches 



(36.8 cm) wide by 10 inches (25.4 cm) deep 
by 4.5 inches (11.4 cm) high. The total mass 
of the computer itself is approximately 10 
pounds (4.54 kg), and can easily be toted 
under one arm along with a typical small TV 
monitor. 

Microprocessor Board 

The BABY! computer comes with a single 
board microprocessor which is mounted 
underneath the keyboard along the bottom 
of the case. The board comes with 2 K bytes 
of static programmable memory, and can be 
expanded to 4 K using sockets on the board 
and additional 2102 memory parts of the 



122 




DELTA ELECTRONICS^ 

POST OFFICE BOX 2, AMESBURY, MASSACHUSETTS 01913 Phone (617) 3884705 

Laboratory Regulated Power Supply 

(VIATROIM System 21) 

This power supply was designed for use in a small computer system 
where performance and reliability were an absolute must. 5 output 
voltages are available: 

1. 12 volts DC<a 1.0 amp 

2. 14 volts DC @ 2.9 amps 

3. 18 volts DC @ 6.6 amps 

4. 26.5 volts DC © 3.25 amps 

5. 24 volts DC@ 1.6 amp 
All voltages are semiconductor rectified and highly filtered, and may be run at full load at the same time. Each output is fused 
seperately, and the entire supply is circuit breaker protected. A switched AC outlet is available on the front panel. This would 
be an ideal supply for a small system; each board could have its own on-board voltage regulators. Also good as a general purpose 
laboratory power supply. Use it stand-alone or rack mounted. 17>2" wide x 5" deep x 6%" high. Shipping weight 35 lbs. 

STOCK NO. B5025 $27.50 each, 2 for $50 




t i 



*.» « - 



*. s 



* 4 






Power Transformer for 13.5v DC @ 10 amps 

This versatile ferro-resonant (voltage regulating) transformer has many uses. With the dual primaries in 
parallel as shown, the DC outputs (after rectification & filtering) are 24v @ 6 amps, 18v (s> 5 amps, and 
13.5v (a> 10 amps. The last is useful for powering CB sets, ham transceivers, and other mobile equipment, 
as well as a computer power supply. By using the 50 Hz taps, voltages are raised about 20%. By using 
the primaries in series, the outputs become 12v DC (g> 6 amps, 9v (s> 5 amps, & 7v @ 10 amps. Either of 
the last 2 could be regulated to +5 volts, making this an ideal computer power supply transformer. 
5%" x 5%" x 514". Shipping weight 24 lbs. With resonating capacitor and data. 

STOCK NO. B9973 $17.95 each, 2/35.00 



G.E. Illuminated Pushbutton Switches 

G.E. illuminated pushbutton switches, with positive action momentary contacts. Snap into panels from front 

without tools, and may be ganged horizontally. Legend inserts can be printed or engraved; they are illuminated 

from the rear with 2 bulbs independent of switch action. Ideal for Reset switches & other control functions, and 

as sense switch inputs. Size: VA" x 7/8", 2J4" behind panel. Takes miniature flange base lamps, up to 28v. Contacts 

rated at 125v max. AC or DC. 

STOCK NO. B6316 SPDT switch Red lens Distributor price $14.60 $4.50 each, 3/12. 

STOCK NO. B6317 DPDT switch Yellow lens Distributor price $17.60 $4.95 each, 3/14.00 




Grab Bags 



Unlike most places, our grab bags are not "floor sweepings. " 
Rather, we offer the same high quality merchandise as in our 
catalog. We attempt to provide a good variety in each bag. 



®zr 



$ffi 



DISC CAPACITOR GRAB BAG. Values from a few pf to .2 mfd 
and voltages from 12v to 1 Kv. Marked, most with long leads. 
STOCK NO. B2547 % lb., 100 to 250 pieces $2.00 ea, 3/5.00 



TERMINAL STRIP GRAB BAG. An assortment of 25 pieces, 

from 1 to 6 terminals, with and without ground lugs. 

STOCK NO. B6143 Package of 25 $1.00 ea, 6/5.00 




*4 WATT RESISTOR GRAB BAG. An assortment of H watt 
resistors on rolls, mostly 10%. Also a few 5% resistors, small diodes, 
rectifier diodes, zeners, & tantalum caps. 250 to 350 parts. 
STOCK NO. B8361 % lb., 250 parts min. $2.00 ea, 3/5.00 

POWER RESISTOR GRAB BAG. An assortment of 4 & 5 watt 
power resistors. STOCK NO. B8765 10 for $1.00, 50 for $3.50 

ELECTROLYTIC CAPACITOR GRAB BAG. 12 assorted 
electrolytics, from 5 mfd to 2500 mfd. Voltages from 5v to 450v. 
STOCK NO. B2457 8 lbs. 12 for $3.00, 36 for 7.50 



Plexiglass 



Quite useful for putting the professional finishing touch on 
your home brew projects. All 3 pieces are 1/8" thick, 
smoked, and have protective paper attached. New. 



STOCK NO. B7295 
one end. 



3" x 17'/4" 



With 54" hole over VA" from 
$2.50 ea, 5/10.00 



STOCK NO. B7325 1 7/8" x 16y 2 ". With %" hole over 1%", 
and small hole over %" on other end. $2.00ea, 5/8.00 



STOCK NO. B7326 
from one end. 



2%' 



x 17 3/8". With %" hole over VA" 
$2.50 ea, 5/10.00 



5 vert, 15 amp Transformer 

A compact, high current transformer, giving 5.0 volts out at 15 amps. 
Use 2 in series for 10v, 15A, which is ideal for the unregulated side 
of a high current, 5v DC logic supply. TA" x 2%" x 3 3/8", 4 lbs. 

STOCK NO. B9979 $4.95 ea., 2/9.00 

RCA End View NUMITR0NS 

The RCA end view NUMITRON is a 7 
segment incandescent readout tube, with 
a character height of 5/8". It requires a 
9 pin Novar socket, which we furnish with 
each tube. The tube operates at a nomi- 
nal voltage of 4.5v, and draws 24 ma. per 
segment. It can be filtered to any color. 
With data. 

STOCK NO. B5207 with sockets $2.75 ea, 4/10.00, 8/18.00 




Send for our latest free catalog. Minimum order $5, phone orders welcome. Include sufficient postage (2 lbs min.), excess will 
be refunded. BANKAMERICARD & MASTERCHARGE welcome, ALL numbers needed for processing. Minimum charge $15. 




Photo 1. 



high speed low power variety. The processor 
board has logic for direct memory access and 
expansion plugs. The system comes with a 
51 2 byte bootstrap loader and firmware 
package in ROM, and has room on the board 
for 4 K oytes of 2708 erasable ROM. 

The processor board features a built-in 
character generator and video interface with 
512 characters organized as 16 lines of 32 
characters. The video interface uses a 7 by 9 
dot matrix character generator with upper 
and lower case plus Greek characters. The 



Photo 2. 




video output is a standard composite video 
signal which can be used to drive a monitor. 
The image is non-interlaced and has low 
flicker. 

Also on the processor board is an audio 
cassette interface which has an effective data 
rate of approximately 1200 bits per second. 

Other details 

The keyboard supplied with the BABY! is 
an upper and lower case commercial alpha- 
numeric keyboard, with 63 keys. Using the 
shift key, standard upper and lower case text 
can be entered. Using the control key, the 
"alternate upper case" of Greek letters can 
be entered and displayed on the video 
monitor output. The standard power supply 
for the unit is 5 V at 3 A, with a 110 VAC 
nominal input, fully regulated. A loud- 
speaker is built in the case to monitor audio 
outputs and allow simple square wave tone 
generation capabilities under program con- 
trol. 

Software 

Don Gunter of STM recently walked into 
the BYTE offices carrying BABY! and a TV 
monitor under his arm as in photo 2, which 
was taken at STM facilities. He opened up 
the brief case, plugged in BABY! and the 
monitor, ran a coax cable from the monitor 
to BABY! and proceeded to load the system 
software on cassette tape using the miniature 
cassette recorder shown in photo 1. Don 
then demonstrated the system. A text mode 
allowed him to type messages up on the 
display ala TV typewriter. An example with 
an advertising message is shown in photo 1 
on the monitor. Then he activated the 6502 
version of Shooting Stars {page 42, May 
1976 BYTE] which is supplied with the 
system. After the frustrated Shooting Stars 
addicts at BYTE had had it out for a while, 
he demonstrated systems software and some 
simple music programs which drive the audio 
output speaker with either random numbers 
or tones selected by a keystroke. 

This neat package will be available in only 
one standard form: a completely assembled 
and tested unit which uses the attache case 
as a key part of its shipping package. It will 
make an excellent teaching system for soft- 
ware concepts in secondary schools and 
colleges, and looks like an excellent system 
for personal use without assembly and con- 
struction hassles. 

You can acquire BABY! by contacting 
STM Systems, Mont Vernon NH 03057. The 
price of the 2 K byte version of BABY! is 
$850, and the same unit with 4 K bytes of 
memory is $1000. STM quotes 60 to 90 day 
delivery after receipt of orders." 



124 



-^CRYSTALS 

, l**^*-' THESE FREQUENCIES ONLY 



Part* 
CY1A 
CY2A 
CY3A 
CY7A 
CY12A 
CY14A 
CY19A 
CY22A 
CY308 



THESE FREQUENCIES ONLY 
Frequency Case/Style 



1.000 MHz 
2.000 MHz 
4.000 MHz 
5.000 MHz 
10.000 MHz 
14. 31818 MHz 
18.000 MHz 
20.000 MHz 
32.000 MHz 



HC33/U 
HC33/U 
HC18'U 
HC18/U 
HC18/U 
HC18U 
HC18/U 
HC18/U 
HC18/U 



Frice 
S4.95 

S4.es 

S4.95 
$4.95 
S4.95 
S4.95 
S4.95 
S4.95 
S4.95 



CLOCK CHIPS — CALCULATOR CHIPS 



MM5309 
MM5311 
MM5312 
MM5313 
MM531-1 
MMS316 
MM5318 

cnooi 

MM5725 
MM5738 
MM 5759 
CT5001 
CT5005 
CT5030 

MM5320 

MM5330 

MM5369 

MM5B41 

MCH08-L7 

MK50Q7 

LDI 10.1011 

95H90 



(i Digil. BCD Outputs, Resei PIN. 
6 Digit. BCD Outputs. 12 01 24 Hour 
4 Digit. BCD Outputs. 1 PPS Oulput 
fi Dfflit, BCD Outputs, 1PPS Output 
6 Digit 12 or 24 Hour. 50 or 60 Hz 
4 Digit Alarm. 1PPS Output 
Video Clock Chip. For Use Wilh MM58-11 
6 Dirji!. Calander. Alarm, 12 or 24 Hour 
CALCULATOR CHIPS 

6 Digit, Four Function, Lrss Decimal 
Digit. 5 Function; +, =, x. -, % 
8 Digit. 4 Function Floating Decimal 
12 Digit 4 Function 

12 Digit. 4 Function with Memory 
12 Digit. 4 Function and *. 

MISC. Ml):; 
IV Camera Sync. Generator 
4'; Digit DVM Chip 

60 Hi Iimehase Circuil From 3 58 MHz 
VttH Generator For MM531B 

7 On Digital to Analog Convener 
4 Decade Counter with Lalches 
3V; Digit DVM Chip Set 

100 MHz - 10 Counter Far Prescalers 



S2.95 
2.95 
2.95 
3 95 
5.95 



10 95 
25 00 
13.95 



FILAMENT TRANSFORMERS 



F-7X 
F-13X * 
M4X>- 



F-25X 
F40X 
F-45X 



VECTOR WIRING PENCIL 



Vector Wiring Pencil P173 consuls of a hand field featherweight ii.nder one ounce) 
tool wnich is used tn guide arid wrap insulated wire, led off a self-contained replaceable 
bobbin, onto comjonent leads or terminals installed an pre-punched "P" Pattern 
Vectorbord' Connections between the wrapped wire and component leads, pads or 
terminals are made by soldering Complete with 250 F ol 



S9.50 



REPLACEMENT WIRE — BOBBINS FOR WIRING PENCIL 
W36-3-A-Pkll 3 250 ft 36 AWG GREEN $2.40 

W36-3-B-Pkg 3 250 It 36 AWG RED S2.40 

W36-3-C-Pko 3 250 II 36 AWG CLEAR S2.40 

W36-3-D-Pkq 3 250 II 36 AWG BLUE S2 40 



*Sv>». 1/16 VECTOR BOARD 



6SIM4Q52XXXP 
169P1J 02XXXP 
64PJ4 062 
84P44 052 
I69P-14 062 
I69P84 062 
I69P44 0H2C1 



VECTOR TER IINALS 



25 pes 50 pes 

Gold Tin Gald Tin 

1 50 foi 1 00 lol 2 75 lot 1 75 lot 

1 75 lot 1 25 lot 3 00 lol 2 25 lot 

1 75 lot l 25 lol 3 10 lot 2 25 Int 



Terminals S3 50 C S13 00M 



DIP SWITCH 



These switches feature seven SPST slide swdcfies in a 
molded dip They are ideally suited lot microprocessor 
applications r. «c 



SCR AND FW BRIDGE RECTIFIERS 



C36D 
C38M 
2N2328 
MDA 980-1 
MDA 980-3 



15Aca400V 
35A @ 200V 
1 6A (§i 200V 



FW BRIDGE REC. 
FW BRIDGE REC 



1 95 



64 KEY KEYBOARD 



Tins keylioaid features 64 une 
coded SPST kevs. unattached 
any kind of PC.B A very solid 
molded plaslic 13" x 4" base 
suits most ao cheat ions 

$19.95 



HDD165 16 LINE TO FOUR BIT PARALLEL KEYBOARD ENCODER 




JOYSTICK 

These joysticks feature four 
100K potentiometers, that vary 
resistance proportional to Ihe 
angle of the stick. Sturdy metal 
construction wilh plastics 
components only at the mova- 
ble joint. Perfect lor electronic 
games and instrumentation. 

$9.95 ea. 



MICROPROCESSOR COMPONENTS 



8080 SUPPORT DEVICES 

8080A 8212 8 BIT INPUT/OUTPUT PORT FOR 8080 
S37 95 8224 CL0CK GENERATOR AND DRIVER FOR 8080 

8228 SYSTEM CONTROLLER AND BUS DRIVER FOR 8080 

CPU'S RAM'S 

8 BIT CPU S19 95 ?60l ?56xi FAST 

Super S008 24 95 HOI !66x 1 Sialic 
A Super BOOB 



2504 
2518 
2519 
2524 
2525 
2527 
2529 
2532 
2533 
3341 
74LS670 



2513 
2516 
74S387 



SR'S 

1024 Dynamic 
He> 32 BTT 
Hen 40 BIT 
512 Dynamc 
1024 Dynamic 
Dual 256 BIT 
Dual 512 BIT 
Quad 80 BIT 
1024 Static 
Filo 
16 > 4 Reg 

UARTS 
3DK Baud 

ROM'S 
Char Gen 
Char. Gen 
1024-Bit Programmanle 



21D1 
2102 
2107 
211! 
7010 



91L02 
74200 
93410 

t rTEA 

5203 
B2S23 
82S123 



Static 

Dynamic 

Sialic 

MNOS 
Static 
Sialic 
Static 
Sialic 
Sialic 
Static 
Sialic 
PROMS 

Famos 
Open C 



S 5 95 8080 
1295 $24.95 

12.95 



S 2 25 
2.95 
6 95 



2K RAM SPECIAL 



MM5262 Fully decoded 2K.nl dynamic RAM All inputs except docks a 
lime, and requires, a +a. +8 5. and —15V power supply Low powe 



riL compatible Provides a 535 ns minimum access 
non volatile memory using battery back up 

SO. 99 ea. (0.05 cents per bit) 



fflff 



"Special Requested Items* 



Wfi 



RC4194 

RC4195 

F9368 

LD110/111 

CA3I30 

MC1408L7 

F3341 

MM5841 

AY5-9100 



Dual Track V Reg 

-15V Track Reg 

Decoder 

DVM Chip Set 

Super CMOS Op Amp 

O/A 

FIFO 



S 5.95 NBT97 S 2.00 MK5007 

3.25 4024P 2 25 8263 

3.95 DM8130 3.25 8267 

25.00 9322 1.30 8288 

1.49 MC14016 .56 B826 

9.95 2525 



2.75 

1.15 
3.00 



2527 



451 1AE 
XR4136 
4566AE 



v.l ll e; k.'-tf-i m uii- ::. ■ '!. yd-;: ■■■■. i -i.-.i. ■--r;-: 



MC4044 

LM3909 

MM5320 

4072AE 

7422 

7497 

74186 

74279 

82S90 

MCT-2E 



Continental Specialties 



PROTO -— 
POWER! 



POWER 

FOR THE 

PROFESSIONAL 



For the economy-minded eipcilmcnlei 

NEW 

Proto Board 100 

utbudkriMiHiiDlhcquil.tvD. -4 f\ ft C 

u>i«h»i« in yn ihemihi- 

.„.,,, .www BREADBOARD 

r , BUDGET KIT 

W 




A Q O A, 

l ( y. 




ii —■■* ■ 

>-.. . ■ — : : ■:■■,. ■■■ ■■- ■ 
' rW «« a * SSW , 1 Mll fll -,,i 
':' . -■ .-■ ■.-:-, ■ ■ ■ , . 
[»».,■•« tBIMndlUdl 10 uwloi 



AUTOTEL ® 
WARNING LIGHTS ARE NOT ENOUGH 




AN AUDIBLE ALARM INDICATING 
POTENTIAL ENGINE DAMAGE 

AUTOTEL is an etfecient [ 15 ma current Standby) device by which every owner ol an 

.liitoiiioliile, truck or vehicle equipped wilfi indicator lights lor temperature and oil 
pressure can be assured ol a reliable warning belnre an impending failure 
AUTOTEL. by means ol an audible signal 70 dli pulsing) immediately forewarns Ihe 
vehicle operator ol a malfunction or (ailue allowing time to correct and prevent maior 
engine failures, ft is progiammed so there is no sound during normal operating 
con dd ions 

AUIOTEL iealures CMOS circuilry. packaged in n 2W" sq. x W case The kit comes 
complete with all components, hardware and case lo hook directly into your car's 
warning light system. 

$14.95 Assembled $9.95 Per Kit 



3% DIGIT DVM KIT 




This 0-2 VDC .05 per cent digital voltmeter features the Motorola 3',i digit 
DVM chip set. It has a 4" LED display and operates from a single + 5V 
power supply. The unit is provided complete with an injection molded black 
plastic case complete with Bezel. An optional power supply is available 
which fits into the same case as the 0-2V DVM allowing 1 1 7 VAC operation, 

A. 0-2V DVM with Case $49.95 

B. 5V Power Supply $14.95 




115 VAC 



JE700 CLOCK 

The JE7O0 is a low cost digital clock. Qui 
is a very high quality unit The unit fea- 
tures a simulated wa'nul case with di- 
mensions ot 6 « 2V*x 1 ll unities a 
MAN72 high brightness readout, and the 
MM5314 clock chip. 

$17.95 



Liquid Crystal Temperature Display 

Six Digit Light q|_ 33 

Emitting Diode Display 

Display 

This clock makes an attractive addition to any desk. II has 
an extruded, black anodized aluminum case. It displays 
hours, minutes, and seconds with .11 inch displays, and 
comes complete with a liquid crystal thermometer. II oper- 
ates off 1 15 VAC at 50 or 60 Hz. $24.95 



•' a : V 9 3 » 



This large digit clock (.6" hours & 
minutes. .3" seconds) features the 
MM5314 clock chip. It operates 
from 117 --C. and will operate in 
either a tfc or 24 hour mode. The 
clock is complete with a walnut 
grain case, and has fast set, slow 
set. and hold time set features, 

KIT - ALL COMPONENTS & CASE S34.95 
WIRED & ASSEMBLED S39.95 



SPECIAL! 



H 



LOGIC MONITOR 

Simultaneously displays static and 

dynamic logic States of DTL. TTL, 

_ HTL or CMOS DIP ICs 

S^ Pocket sue SBa.95. 




QT Prolo SI dps 



;qt-ibs 

OT-12S 



OTIype 

QT-59S 

QT-599 

OT-47S 

OT-47B 

QT-355 

OT-35B 

OT IBS 

QT-125 

QT-8S 

QT-7S 



DIGITAL CLOCK KIT — 3 1 / 2 INCH DIGITS 




4 DIGIT KIT $49.95 
6 DIGIT KIT S69.95 



4 DIGIT ASSEMBLED S59.95 
6 DIGIT ASSEMBLED S79.95 



clock Iealures Dig 3l> ' high digits 
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JE803 PROBE 

the Logic Probe is a unit winch is tor the most part 
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NIBBLING TOOL DIAGONAL CUTTER 

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C & K Rocker Switch SPOT 

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MAN 7G Common Anode-Green .3" DISPLAY LED 

6' Black 3 Conductor Power Supply Cords 

LM309KC 

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Primary: 120 VAC @ 50 Hz-60 Hz. Secondary: 
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Articles Policy 

BYTE is continually seek- 
ing quality manuscripts writ- 
ten by individuals who are 
applying personal systems, or 
who have knowledge which 
will prove useful to our read- 
ers. Manuscripts should have 
double spaced typewritten 
texts with wide margins. Num- 
bering sequences should be 
maintained separately for fig- 
ures, tables, photos and list- 
ings. Figures and tables should 
be provided on separate sheets 
of paper. Photos of technical 
subjects should be taken with 
uniform lighting, sharp focus 
and should be supplied in the 
form of clear glossy black and 
white prints (if you do not 
have access to quality photog- 
raphy, items to be photo- 
graphed can be shipped to us 
in many cases). Computer list- 
ings should be supplied using 
the darkest ribbons possible 
on new (not recycled) blank 
white computer forms or bond 
paper Where possible, we 
would like authors to supply a 
short statement about their 
background and experience. 

Articles which are accepted 
are typically acknowledged 
with a binder check 4 to 8 
weeks after receipt. Honorari- 
ums for articles are based 
upon the technical quality and 
suitability for BYTE's reader- 
ship and are typically $15 to 
$30 per typeset magazine 
page. We recommend that au- 
thors record their name and 
address information redun- 
dantly on materials submitted, 
and that a return envelope 
with postage be supplied in 
the event the article is not 
accepted. • 



Continued from page 4 

BYTE for details.] He then asked interested 
people to see him during the random access 
session later. 

The reason for describing this dynamic 
process is to emphasize that it works, that it 
breeds great enthusiasm in its participants, 
and that it provides a valuable service. Based 
on my experience in observing one such 
session, I highly recommend a mapping 
session for any club so large that meeting 
people and finding out their current interests 
is not an instantaneous process — say, a 
session with more than 20 to 30 persons. 

One or many? 

In an editorial in the January issue, I 
suggested that the Southern California Com- 
puter Society was looking upon itself as a 
possible national organization for computer 
people. Well, that conclusion was based 
upon evidence of their publication, Interface 
(far too grandiose for a merely regional 
operation) and attempts to sign up chapters 
everywhere. I have since that time gotten 
feedback of "Who needs a national organi- 
zation?" from other individuals and sources. 
The following points of view were in part 
elucidated by Sol Libes of the Amateur 
Computer Group of New Jersey and Gary 
Coleman of the Midwest Affiliation of Com- 
puter Clubs in conversations May 1 and May 
2 at the Trenton Computer Festival this 
year. 

There is a counter argument to the idea 
that computer users need a national organi- 
zation like the Amateur Radio Relay 
League. The ARRL has a definite need for 



Tool Box Answers 




Here are the tools and fasteners hidden in 


Bob Baker's "Tool 


Box" [page 39, July 


BYTE]. Watch for 


more "Baker Street 


Irregulars" in future BYTEs. 


ALIGNMENT 


PLIER 


AWL 


PUNCH 


BRUSH 


REAMER 


CENTERPUNCH 


RIVET 


CUTTER 


RULER 


DIE 


SAW 


DIKES 


SCISSORS 


DRILL 


SCRIBER 


FILE 


SHEAR 


FORCEPS 


SOLDER 


HAMMER 


SQUARE 


KNIFE 


TAP 


LATHE 


TWEEZERS 


MICROMETER 


VISE 


MOTOTOOL 


WIRECRIMPER 


NEEDLENOSE 


WIRESTRIPPER 


NIBBLER 


WJREWRAP 


NUT DRIVERS 


WRENCH 



its existence in amateur radio because a 
central bureaucratic entity, the FCC, exists in 
the US government; and its regulations 
vitally affect amateur radio. There is no 
parallel to the FCC in amateur computing, 
because computers are fundamentally self 
contained and cannot block other users from 
access in the same way that a radio station 
can jam another station on the same fre- 
quency. It is not likely that there will be any 
such regulatory agency for computers, so 
there is no central need as there is in 
amateur radio. (Of course, the computer 
hackers who are also radio amateurs and 
want to develop various radio data exchange 
techniques must deal with the FCC; but here 
established amateur radio organizations such 
as the ARRL already exist.) 

An argument against the very concept of 
a nationwide organization is not only "Who 
needs it?", but "Why should our nice local 
club become a cog in someone else's bureau- 
cratic empire?" This is perhaps the most 
powerful argument, for unless there is a 
specific goal to be accomplished at a 
national level, the real purposes of computer 
clubs are best served by the local groups 
which are springing up across the nation. 
Gary Coleman and Sol Libes both argued 
that the highest level of organization they 
could see as a useful concept might be 
regional affiliations of clubs for organizing 
computer fests and other cooperative events. 
About the only nationwide extension of this 
concept might be the idea of holding a 
national conference of small computer users 
and manufacturers. Such affiliations are pro- 
posed as fairly informal affairs carried out 
by correspondence and telephone, with 
representatives travelling back and forth as 
business and travel plans permit. 

This all leads back to the "real purposes" 
of computer clubs. These are perhaps best 
served by small, informal clubs of a local 
nature whose goals are enjoyment and social- 
ization on computer themes. Examples are 
the friendly and informal atmosphere of the 
Homebrew Computer Club meeting cited 
above, as well as the inevitable conversations 
which occur at local meetings. In some of 
the smaller computer clubs, for example the 
Nashua NH group, the meetings are devoted 
exclusively to informal "bull sessions" on 
one or two topics of technological interest. 

I'm not going to draw any conclusions 
one way or the other on this issue, but 
would like to see some inputs from readers 
by way of the letters section of BYTE. What 
positive reasons are there for a national 
computer group? What are the negative 
reasons? What are the arguments for keeping 
the whole idea of computer clubs a local 
affair?" 



126 




POWER SUPPLY MODULE 

New, plug-in module. Plugs into AC outlet 
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POWER SUPPLY 

LAMBDA 5VDC 74 AMP 

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NJE 5/OUP-D5 
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3 Power supplies, transistorized & regulated. 
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1 5 volts DC 5 amps $25.00 

30 volts DC 2 amps 25.00 

1 5 volts DC 4.5 amps 25.00 



CLOCK KIT $14.00 

Includes all parts with MM5316 chip, 
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everything except case. 

SP-284 $14.00 each 2/$25.00 




VIDEO DISPLAY, Spares from VIATRON system. 9 inch 
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COMPUTER GRADE LOGIC SUPPLY CAPS, BRAND NEW 

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DUMMY LOAD RESISTOR, non inductive, 50 ohm 5 watt 
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MEMORY SYSTEM $125.00 

New memory system by Honeywell, small . . . 
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Ship wgt 3 lbs. #SP-79 $125.00 

CORE MEMORY 

Another brand new memory, ultra small. Measures only 4x4 inches 
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FREE CATALOG SP-8 NOW READY 

Please add shipping cost on above. 

MESHNA P0 Bx 62 E. Lynn Mass. 01904 



127 



EWE 

reader 
service 



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* 


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A22 


National Multiplex 59 


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A64 


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A41 


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A85 


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# 


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Tri Tek115 



'Reader service inquiries not solicited. Correspond directly with company. 



BOMB: 



May's BOMB Winner 

Winner of the $50 prize for the most 
popular article in the May 1976 issue of 
BYTE is Roger Frank's "Microprocessor 



Based Analog/Digital Conversion Tech- 
niques." Runners-up in the voting were 
"More Information on PROMs" by Roger 
Smith, and "Simplify Your Homemade As- 
sembler" by Gregory C Jewell. 



BYTE's Ongoing Monitor Box 

Feedback is what keeps a linear amplifier in line. Like a linear amplifier, B YTE can use a bit 
of feedback. The BOMB analysis is done once a month to provide encouragement to authors 
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that with few exceptions BYTE authors are just readers who have sat down at their typewriters 
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technology. 



LIKED 



PAGE ARTICLE 

6 Buchanan: What Do You Do With a Video Disk? 
16 Rice: Friends, Humans, Country robots: Lend me your Ears 
26 At mar : The Time Has Come to Talk 
34 Hashizume: Microprocessor Update: Zilog Z80 
40 Wadsworth: "8008" Programming-Chapter 2 
44 Gupta: True Confessions: How I Relate to KIM 
52 Grappel-Hemenway: Jack and the Machine Talk 
66 Suding: Build a TV Readout Device for Your Microprocessor 
84 Steeden: What's an l 2 L (I squared L)7 
96 King: Interfacing the 60 mA Current Loop 



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128 




we started at the top 
and worked our way up! 



■ ( 




HVj 



m 



! I 



■ I I 



And we're still working. We were 
first in the microprocessor computer 
field to offer a CPU in a complete 
system. A microprocessor with a . 
method of inputing information, 
processing data and providing 
meaningful output. 

But we didn't stop there. We had 
the best product on the market... 
but we didn't have the best product 
possible. So our engineers went 
to work. Through research and 
development a good machine got 
better. We've added more memory 
and versatility in a rapid succession 
of advancements. And everything is 
compatible with the basic product 
without extensive internal changes. 



We're still on top in the micro- 
processor field... and through 
research and development we'll stay 
on top. At Sphere we're committed 
to engineering leadership, because 
in the microprocessor field, you're 
only on top as long as you're 
working your way up. 

Write for complete information: 



Sphere Corporation 
Dept. 102 
P.O. Box 213 
Bountiful, Utah 84010 



■■ 



SPHERE 

CORPORATION 



■ 






Measuring just 11" wide x 11" deep x 5" high, and weighing a 
mere 7 pounds, the Altai r ™ 680b is a complete, general-purpose 
computer. 

The secret to this revolutionary, small computer is its CPU 
board. This double-sided board fits along the bottom of the Altair 
case and plugs directly into the front panel board. It contains 
the new 6800 microprocessor, 1,024 bytes of RAM memory, a 256 
byte PROM monitor, provisions for 768 bytes of additional PROM 
or ROM, and a single Interface port with a Motorola ACIA serial 
interface adapter which can be configured either RS-232 or TTY. 
A five level Baudot interface option is also available. 

The Altair 680b can be programmed from front panel switches, 
or it can be interfaced to a video display terminal, or teletype- 
writer. Three additional circuit boards can be plugged inside the 
Altair 680b for further memory and interface expansion. The first 
of these boards is a 16K static RAM memory board. 

Software already developed includes Altair 680 BASIC with 
all the features of the 8K BASIC previously developed for the 
Altair 8800. These include Boolean operators, the ability to read 
or write a byte from any I/O port or memory location, multiple 
statements per line, and the ability to interrupt program execution 
and then continue after the examination of variable values. This 
software takes only 6.8K bytes of memory space and a copy is 
included free with the purchase of the Altair 680 1(>K memory 
board. 

Other software includes a resident two pass assembler. The 
Altair 680b is also compatible with Motorola 6800 software. 

The Altair 680b is ideal tor hobbyists who want a powerful 
computer system at an economic price. Altair 680b owners qualify 



for membership in the Altair Users Group, and like other Altair 
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Notes and complete factory support. 

PRICES: 

Altair 680b kit with complete, easy-to-understand assembly man- 
ual, operator's manual, and programming manual $466 

Assembled Altair 680b $625 

Altair 680b Turnkey model kit 395 

Expander Card 680MB (required to expand 680) $ 24 

Altair 680BSM 16K static RAM board kit with 680 BASIC $685 
Altair 680 BASIC when purchased separately $200 

Baudot option $ 42 

MAIt THIS COUPON TODAY 



□ Enclosed is a (heck for $_ 

□ BanltAmericard = 



or Master Charge ~ 

□ Altair &80b □ Kit D Assembled □ Other (specifv) 
enclose $8 for postage and handling 

□ Please send tree information package. 



ADDRESS- 
CITY 



-STATE & ZIP_ 



G§ DlDDl^ 



2450 Alamo SE/Albuquerque, NM 87106, 50S-243-7821 



NOTE: Altair is a trademark of MITS, Inc. 



Price, specifications subject to change. Please allow up to foO days for delivery. 



.